US20080111985A1 - Camera based six degree-of-freedom target measuring and target tracking device - Google Patents
Camera based six degree-of-freedom target measuring and target tracking device Download PDFInfo
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- US20080111985A1 US20080111985A1 US11/738,005 US73800507A US2008111985A1 US 20080111985 A1 US20080111985 A1 US 20080111985A1 US 73800507 A US73800507 A US 73800507A US 2008111985 A1 US2008111985 A1 US 2008111985A1
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/16—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using electromagnetic waves other than radio waves
- G01S5/163—Determination of attitude
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/002—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates
Definitions
- the present disclosure relates to a coordinate measuring device.
- One set of coordinate measurement devices belongs to a class of instruments that measure the three-dimensional coordinates of a point by sending a laser beam to the point.
- the laser beam may impinge directly on the point or may impinge on a retroreflector target that is in contact with the point.
- the instrument determines the coordinates of the point by measuring the distance and the two angles to the target.
- the distance is measured with a distance-measuring device such as an absolute distance meter or an interferometer.
- the angles are measured with an angle-measuring device such as an angular encoder.
- a gimbaled beam-steering mechanism within the instrument directs the laser beam to the point of interest.
- Exemplary systems for determining coordinates of a point are described by U.S. Pat. No. 4,790,651 to Brown et al. and U.S. Pat. No. 4,714,339 to Lau et al.
- the laser tracker is a particular type of coordinate-measuring device that tracks the retroreflector target with one or more laser beams it emits.
- a coordinate-measuring device that is closely related to the laser tracker is the laser scanner.
- the laser scanner steps one or more laser beams to points on a diffuse surface.
- a second set of coordinate measurement devices belongs to a class of instruments that measure coordinates using one or more cameras to view points of light attached to a probe. Cameras view these points of light and from the images determine the position of the probe tip. In most cases, two or more cameras are used. These cameras may be rigidly connected, or they may be set up individually according to the particular measurement requirements. If the cameras are not rigidly connected, a reference length must be measured by the cameras either before or during the measurement to establish the scale.
- An exemplary system for determining the coordinates of a point using cameras and points-of-light is described by U.S. Pat. No. 5,196,900 to Pettersen.
- a rangefinder comprises a distance meter and one or more steering mirrors.
- the rangefinder measures the distance to a retroreflector mounted on a probe.
- a camera positioned near the rangefinder measures the angles to point light sources located on the probe. The combination of distance and angle information gives the coordinates of the probe tip.
- a rangefinder comprises a distance meter and one or more steering mirrors. The rangefinder directs light to a retroreflector mounted on a probe.
- Laser trackers though highly accurate and fast, are too expensive for many common operations such as precisely positioning robot end effectors to drill holes.
- laser trackers measure only three-dimensional coordinates rather than all six degrees of freedom. Because of this, laser trackers must in some cases measure three or more targets to find all six degrees of freedom. Measuring multiple targets in this way requires additional time and targets.
- Camera-based coordinate measurement devices based on two or more cameras are also expensive and also have geometrical limitations. To be accurate, individual cameras must be spaced relatively far apart compared to the measurement range. Consequently, camera systems are limited in their ability to see into narrow openings. Camera systems also have a limited field-of-view, which means that time-consuming relocation procedures may be necessary to view all targets within the measurement volume.
- An embodiment may comprise a camera based target coordinate measuring system and/or apparatus for use in measuring the position of objects in manner that preserves a high level of accuracy.
- This high level of measurement accuracy is usually only associated with more expensive laser based devices. Many different arrangements are possible.
- Another embodiment may comprise a camera based coordinate measuring system for use in measuring the position of a target relative to at least one frame of reference without requiring use of a laser range finder for measuring distance comprising: at least three or more light sources located on a target at known three-dimensional coordinates relative to each other; at least one rotatable camera rotatable on about a first axis and a second axis wherein the camera records positions of the light sources; and two angular measuring devices to measure the angles of rotation of the camera about the first and second axes; and a processor for determining up to three positional degrees of freedom and up to three rotational degrees of freedom of the target.
- Other embodiments may comprise related methods of using a camera based target coordinate measuring method for use in measuring the position of objects. Many variations of the methods are possible.
- one specific method comprises, a camera based target coordinate measuring method for use in measuring the position of objects without requiring use of a laser range finder for measuring distance comprising: operating a camera rotatable about a first axis and a second axis; placing a target to view with the camera and having at least three or more light sources wherein the light sources are located on the target at known three-dimensional coordinates relative to each other and wherein at least one of the light sources is located at a different distance from the camera than the midpoint of a line segment connecting two of the other light sources, and wherein the target is structured to be placed on an object to be measured or to be placed on a device to measure the object; measuring angles of rotation of the camera about the first and second axes with two angular measuring devices; rotating the camera about the first and second axes with at least one motor; recording the images of the light sources on a photosensitive pixel array located in the camera; and determining in a processor up to three positional degrees of freedom and up to three rotational degrees of freedom of
- FIG. 1 is a perspective view of an exemplary three-dimensional measuring device and system
- FIGS. 2A and 2B are perspective views of exemplary targets 200 A and 200 B.
- FIGS. 3A-3F are perspective views of exemplary targets 200 A and 200 B and 200 C and 700 ;
- FIGS. 4A and 4B are perspective and front views of exemplary target 1200 ;
- FIGS. 5A-5F are perspective views of exemplary targets 1200 .
- FIG. 6 is a perspective view of an exemplary referenced hand-held scanner 1800 .
- FIG. 7 is a perspective view of an exemplary referenced articulated arm CMM 2000 .
- FIG. 8 is a perspective view of the internals of one possible embodiment of camera 140 with cylindrical lenses.
- FIG. 9 is a perspective view of the internals of another possible embodiment of camera 140 with a spherical lens.
- FIG. 10 is a schematic representation of another possible embodiment of camera 140 with spherical lens and two beam paths.
- an exemplary six degree of freedom (6-DOF) tracker 1000 may comprise a rotating tracking camera 100 , target 400 , and computer 300 .
- Six degrees of freedom may be the x, y, z coordinates, and the pitch, roll, and yaw of target 400 for example.
- Overall tracking camera apparatus 100 may comprise first-angle assembly 120 , second-angle assembly 130 , camera 140 , and processor 150 .
- First-angle assembly 120 comprises first-angle shaft (not shown) onto which are mounted angle meter 122 and motor 124 .
- Angle meter 122 is preferably an angular encoder and motor 124 is preferably a servo-motor.
- First-angle shaft (not shown) rotates around first axis 126 , which in this figure is the zenith axis. The first and second axes intersect at a point in space called the gimbal point.
- Second-angle assembly 130 comprises second-angle shaft (not shown) onto which are mounted angle meter 132 and motor 134 .
- Angle meter 132 is preferably an angular encoder and motor 134 is preferably a servo-motor.
- Second-angle shaft (not shown) rotates around second axis 136 , which in this figure is the azimuth axis.
- Camera 140 is mounted on first-angle assembly 120 .
- First angle assembly and camera rotate about first axis 126 .
- First angle assembly is mounted on second-angle assembly.
- Second-angle assembly 130 rotates with respect to the base about second axis 136 .
- the camera 140 shown in the FIG. 1 is well known. All that is necessary is that it is possible to direct the camera 140 to point at any direction within the measurement volume. Any two angular rotations can be used to obtain the desired imaging of target 200 B on the camera.
- Targeted end effector 400 comprises end effector 410 and one or more of target 200 B in this example.
- End effector 400 may be mounted on a robot arm or machine tool for example.
- Tool 412 which may be a drill bit, mill, or any other attachment, is connected to end effector 410 .
- FIG. 1 merely shows one of many possible configurations.
- camera 140 The purpose of camera 140 is to form an image of target 200 B on a photosensitive array within the camera and to read out the values on this array for analysis so that the position of tool 412 can be precisely controlled.
- tool 412 can be controlled even when it is not visible to camera 140 so long as target 200 B is visible.
- Processor 150 uses image intensity values from pixels of camera 140 and angle data from angle meters 122 and 132 to calculate the six degrees of freedom of target 400 . Processor 150 also sends control signals to motors 124 and 134 to move the camera into the desired position.
- position control There are three types of position control that can be selected by the user: (1) tracking position control, (2) user-specified position control, and (3) manual position control. If tracking position control is selected, processor 150 causes the motor to be adjusted to keep target 200 approximately centered on the photosensitive array(s) within camera 140 . If user-specified position control is desired, processor 150 causes motors to drive mirror to the direction selected by the user. If manual position control is desired, motors 124 and 134 are turned off, allowing the user to manually point the mirror in the desired direction.
- target 200 comprises at least three points of light at fixed positions relative to one another. In general, by using more than 3 points, it is possible to maintain high radial accuracy over an extended range.
- target 200 A which is a first embodiment of target 200 , comprises points of light 210 , 211 , and 212 , pedestal 220 , and base 230 .
- Points of light are preferably LEDs but may be other types of active light sources or may also be passive reflectors.
- An example of a passively reflector is a photogrammetric spot that is illuminated by flashing lights located in the vicinity of 6-DOF tracker 1000 .
- Target 200 B which is a second embodiment of target 200 , comprises seven points of light 240 - 246 , five pedestals 250 - 254 , and base 260 .
- additional points of light on target 200 B are turned on as target 200 B moves away from 6-DOF tracker 1000 with camera 140 .
- points of light 242 , 243 , and 244 illuminate.
- points of light 241 and 245 also illuminate.
- additional points of light 240 and 246 also illuminate Alternatively, all seven points of light may be illuminated at all times, with more points of light coming into view as distance is increased.
- base 230 or 260 is attached to some other object whose six degrees of freedom are to be measured.
- Pedestals such as 220 and 250 - 254 provide a geometry that is favorable for high accuracy measurement of radial distance to the object.
- a light source is mounted onto a pedestal so that its axis of emission is approximately in line with the axis of the pedestal.
- Camera 140 points at a target, which may be 200 B, for example, as shown in FIG. 1 .
- the axis of camera 140 is kept more or less in line with the axes of the pedestals.
- a good rule of thumb is that the optical axis of camera 140 should be within ⁇ 45 degrees of the pedestal axes. As explained in the section on System Accuracy, the best accuracy is obtained when the angle is zero degrees.
- a good choice for light sources 210 - 212 and 240 - 246 are LEDs that emit over a wide field of view. LEDs that emit over a full-angle of 110 to 120 degrees are readily available.
- the pedestals are preferably tall enough so that the higher pedestals do not clip the light emerging from the lower pedestals. Also the pedestals should be tall enough to provide sufficient accuracy.
- a good rule of thumb is that the pedestals should be tall enough to produce an angle of at least 20 degrees between base 230 and the line of light sources 210 , 211 or between base 260 and the line of light sources 240 - 243 . The advantage of having a large enough angle will be made clear in the section on System Accuracy.
- targets 200 A and 200 B have points of light mounted on pedestals that are higher at the center and lower at the edges, it is equally possible to place the higher pedestals at the edges and the lower pedestals nearer the center.
- the accuracy of the pitch and yaw angles also increases.
- a target having at least three or more light sources wherein the light sources are located on the target at known three-dimensional coordinates relative to each other and wherein at least one of the light sources is located at a different distance from the camera than the midpoint M of a line segment S connecting two of the other light sources, and wherein the target is structured to be placed on an object to be measured or to be placed on a device to measure the object. See FIG. 2 .
- Points of light 210 - 212 in 200 A and 240 - 246 in 200 B are coplanar and appear to form a straight line when viewed from a certain direction. This pattern was selected because its principle of operation is easy to explain. However, in general, the light sources can be arranged in a variety of patterns without sacrificing accuracy. It is not necessary that all of the points be coplanar or that they appear to form a straight line when viewed from a particular direction.
- the spots of light on the photosensitive array within camera 140 will not fill the array. In other words, the spots of light will not extend from the far left side of the array to the far right, nor will they extend from the lower edge to the upper edge. Instead, some smaller fraction of the array is usually covered. Another way of saying this is that only a fraction of the available range of pixels along a given direction in the array is subtended by the spots of light in the image. As explained in the section on System Accuracy, the relative uncertainty in radial distance measurement of 6-DOF tracker 1000 is proportional to the fraction of the photosensitive array in the camera subtended by the points of light from the target 200 B for example.
- target 200 B moves away from 6-DOF tracker 1000 , the fraction of the array subtended by points of light decreases, causing the relative accuracy to decrease proportionately.
- the relative accuracy is restored.
- the light sources in target 200 B are spaced such that size of the target visible to camera 140 increases by a factor of 2 each time two new spots of light appear in the camera image.
- LEDs 242 , 243 , and 244 nearly fill the photosensitive array when target 200 B is 1 meter from 6-DOF tracker 1000 .
- the accuracy drops—for example, from 5 to 10 ppm, as explained in the section on accuracy below.
- points of light 241 and 245 also turn on. This restores the accuracy to 5 ppm.
- points of light 240 and 246 also turn on. In this way, it is possible to maintain a relative accuracy in the radial distance measurement of 5 to 10 ppm over the range of 1 to 8 meters.
- targeted end effector 400 comprises end effector 410 and one or more of embodiment target 200 B. (Target 200 A could equally well have been used.) End effector 400 may be mounted on a robot arm or machine tool for example. Tool 412 , which may be a drill bit, mill, or any other attachment, goes on end effector 410 .
- probe 500 comprises probe body 510 , shaft 520 , tip 530 , and one or more targets 200 A. (Target 200 B or any other collection of three or more points could equally well have been used.)
- the 6-DOF tracker calculates the coordinates of probe tip 530 .
- Probe tip 530 may be inserted inside holes or behind objects that are not visible to the camera in 6-DOF tracker 1000 .
- Probe 500 may take any shape. The probe may be tilted in any direction or bent into any shape.
- Probe body 510 may be any length.
- tooling-hole fiducials 600 sit inside tooling holes (not shown) that have been drilled in a tool or work piece to serve as fiducial (reference) points.
- the purpose of tooling-hole fiducials is to enable determination of the coordinates of the tooling hole.
- This information may be used to establish the frame of reference of the measuring instrument in terms of the global coordinates of the tool or work piece. This information may also be used to check for changes in the work piece caused by thermal expansion or similar effects.
- Tooling-hole fiducial 610 comprises shank 612 , body 614 , and vertical target 200 A.
- Shank 612 sits inside the tooling hole.
- Tooling-hole fiducial 620 comprises shank 622 , body 624 , and horizontal target 200 A.
- Tooling-hole fiducial 630 comprises hemisphere 632 , nest 640 , and target 200 C.
- Target 200 C is like target 200 A except that the pedestals are located beneath the outermost points in target 200 C rather than the innermost as in target 200 A.
- On the bottom of nest 640 is a shank (not shown) that sits inside a tooling hole.
- the center point of light of target 200 is located at the spherical center of hemisphere 632 so that its coordinates do not change as hemisphere 632 is rotated.
- the purpose of having three different types of tooling-hole fiducials is to provide an appropriate viewing angle for 6-DOF tracker 1000 .
- any number of tooling-hole fiducials may be used depending upon the application.
- Spherical target 700 comprises spherical body 712 and points of light 714 and central point of light 716 .
- Central point of light 716 is located at the spherical center of spherical body 712 .
- central point of light 716 remains fixed.
- Spherical target 700 may be moved over any object as a way of determining the coordinates of points of an entire surface or multiple surfaces. Because the distance from the spherical center and the surface being touched by target 700 is a known constant value, the coordinates of the surface being measured can be determined. From the collected data, characteristics of the object such as flatness, perpendicularity, diameter, and so forth can be found.
- a nest 800 can be attached to the surface at various points.
- the nest provides a convenient alternative to tooling holes for establishing fiducial locations.
- Spherical target 700 has four light sources 714 along the upper surface of spherical body 712 .
- Two light sources 714 in addition to light source 716 , are sufficient to determine the angles and distance to the center of sphere 716 .
- the additional two points of light 714 (four rather than two) have been added to improve accuracy.
- two sources of light 714 and one source of light 716 are sufficient to provide the pitch, roll, and yaw angles of spherical target 700 .
- point of light 716 is located in the center of a spherical surface, pitch, roll, and yaw angles are not ordinarily required to make measurements with spherical target 700 .
- target 1200 comprises mount 1210 ; pedestals 1271 - 1274 , 1281 - 1284 ; and point sources of light 1220 - 1234 , 1241 - 1244 , 1251 - 1254 , 1261 - 1264 .
- Mount 1210 and pedestals 1271 - 1274 , 1281 - 1284 are preferably made of a material having a low thermal coefficient of expansion such as Invar.
- Point sources of light 1220 - 1234 , 1241 - 1244 , 1251 - 1254 , and 1261 - 1264 are preferably light-emitting diodes that are not covered by glass, epoxy, or similar material, unobstructed by bonding wires, and having a wide angle of emission.
- point sources of light 1220 - 1234 , 1241 - 1244 , 1251 - 1254 , and 1261 - 1264 may be photogrammetric targets illuminated by an external source of light. Point sources of light are located either along circle 1230 or 1250 . When target 1200 is relatively far from tracking camera 100 , point sources of light 1251 - 1254 , 1261 - 1264 along the outer circle 1250 and point source of light 1220 are illuminated. When target 1200 is too close to 6-DOF tracker 1000 for all LEDs along outer circle 1250 to be simultaneously viewed by the photosensitive array within 6-DOF tracker 1000 , then point sources of light 1231 - 1234 , 1241 - 1244 along inner circle are illuminated.
- Target 1200 has eight point sources of light along circle 1230 and eight points of light along circle 1250 . This compares to only two equivalent points in targets 200 A, 200 B, and 200 C. This factor-of-four increase in the number of point sources of light causes accuracy to increase by a factor of approximately the square root of four. In other words, the accuracy of target 1200 is expected to be approximately two times better than that of targets 200 A, 200 B, and 200 C.
- additional circles of LEDs may be placed inside circle 1230 or outside circle 1250 .
- targeted end effector 1300 comprises end effector 1310 and target 1200 .
- End effector may be mounted on a robot arm or machine tool for example.
- Tool 1312 which may be a drill bit, mill, or any other attachment, goes on end effector 1310 .
- probe 1400 comprises probe body 1410 , shaft 1420 , tip 1430 , and target 1200 .
- the 6-DOF tracker 1000 calculates the coordinates of probe tip 1430 .
- Probe tip 1430 may be inserted inside holes or behind objects that are not visible to the camera in a 6-DOF tracker 1000 .
- Probe 1400 may take any shape. The probe may be tilted in any direction or bent into any shape.
- Probe body 1410 may be any length. The length will be a known dimension.
- tooling-hole fiducials 1500 sit inside tooling holes (not shown) that have been drilled in a tool or work piece to serve as fiducial (reference) points.
- the purpose of tooling-hole fiducials is to enable determination of the coordinates of the tooling hole.
- This information may be used to establish a frame of reference of the measuring instrument in terms of the global coordinates of the tool or work piece. This information may also be used to check for changes in the work piece caused by thermal expansion or similar effects.
- Tooling-hole fiducial 1510 comprises shank 1512 , body 1514 , and vertical target 1200 .
- Shank 1512 sits inside the tooling hole.
- Tooling-hole fiducial 1520 comprises shank 1522 , body 1524 , and horizontal target 1200 .
- Tooling-hole fiducial 1530 comprises hemisphere 1532 (hidden from view in FIG. 5E but having the same shape as hemisphere 632 in FIG. 3E ), nest 1540 , and target 1200 .
- On the bottom of nest 1540 is a shank (not shown) that sits inside a tooling hole.
- the center point of light of target 1200 is located at the spherical center of hemisphere 1532 so that its coordinates do not change as hemisphere 1532 is rotated.
- the purpose of having three different types of tooling-hole fiducials 1500 is to provide an appropriate viewing angle for 6-DOF tracker 1000 .
- Spherical target 1600 comprises spherical body 1612 and target 1200 .
- the point of light 1220 centered in target 1200 is located at the spherical center of spherical body 1612 .
- point of light 1220 remains fixed.
- Spherical target 1600 may be moved over any object as a way of determining the coordinates of points of an entire surface or multiple surfaces. Because the distance from the spherical center and the surface being touched by target 1600 is a known constant value, the coordinates of the surface being measured can be determined. From the collected data, characteristics of the object such as flatness, perpendicularity, diameter, and so forth can be found.
- a nest 1700 can be attached to the surface at various points. The nest provides a convenient alternative to tooling holes for establishing fiducial locations.
- FIG. 6 shows another embodiment of target 1200 .
- Referenced scanner 1800 comprises target(s) 1200 located on one or more faces of hand scanner body 1810 that is attached to hand scanner grip 1820 .
- An operator holds hand scanner grip 1920 while pointing reference scanner 1800 at object-under-inspection 1900 .
- Referenced scanner 1800 generates laser-line 1830 that strikes object-under-inspection 1900 , thereby scattering light that is picked up by electro-optic detecting components (not shown) within referenced scanner. From this detected light, referenced scanner determines the three-dimensional contour of object-under-inspection 1900 relative to its own internal frame of reference.
- 6-DOF tracker 1000 measures the six degrees of freedom of referenced scanner 1800 and uses this information to transform the scanned data into the global frame of reference. In this way, the operator can move referenced scanner 1800 to any location within the range of rotation of 6-DOF tracker 1000 . The result is a contour of the entire object-under-inspection 1900 within the global frame-of-reference.
- hand scanner body 1810 An alternative to mounting targets 1200 (or other targets such as 200 A, 200 B, or 200 C) onto hand scanner body 1810 is to build the mounts for the point sources of light directly into hand scanner body 1810 .
- hand scanner body can be molded of carbon fiber composite, thereby achieving a stable mount with a very low coefficient of thermal expansion (CTE) for relatively low cost.
- CTE coefficient of thermal expansion
- targets 1200 , 200 A, 200 B, and 200 C for the point sources of light, it should be understood that there are many suitable ways of arranging the point sources of light on the surface of hand scanner body 1810 and that the arrangements described here are not to be construed as limiting to the design.
- a variant of the hand scanner shown in FIG. 6 is a scanner like that shown in FIG. 6 but mounted on a robotic structure (that is not held by hand).
- the robotic structure may be one that has many degrees of freedom, and in this case the scanner is mounted on the robot end effector.
- the scanner may be mounted on a robotic structure that moves rectilinearly.
- This rectilinear structure may be a simple motorized rail that moves in one dimension or a gantry structure that moves in two or three dimensions.
- points of light are mounted on the robotic structure in such a way as to permit inspection data collected by the scanner to be transformed into the global frame of reference.
- FIG. 6 shows an exemplary method of mounting the points of light onto the scanner that is attached to a robotic structure. In this case, however, grip 1820 would be removed and targets 1200 would be attached directly to the robotic structure.
- FIG. 7 shows another embodiment of target 1200 .
- Referenced articulated-arm coordinate measuring machine (CMM) 2000 comprises articulated-arm CMM 2010 and target 1200 .
- Articulated-arm CMM 2010 comprises stationary base 2012 , a plurality of rotatable segments 2014 A- 2014 F, probe tip 2016 , and angular encoders 2018 (internal components that are not visible in FIG. 7 ).
- the operator brings probe tip 2016 into contact with the object-under-inspection (not shown).
- Angular encoders 2018 are located at each joint. They measure the angles of rotatable segments 2014 A- 2014 F, and these angles are used to calculate the position of probe tip 2016 to high accuracy.
- Each articulated-arm CMM 2010 has a certain maximum reach that is determined by the combined length of the individual rotatable segments. To measure large objects-under-inspection, it is necessary to move articulated-arm CMM 2010 to multiple locations. Traditional methods for doing this such as measuring multiple target nests in a piggyback fashion can be time consuming and inconvenient. This problem is eliminated when 6-DOF tracker 1000 images light emitted by target 1200 in referenced articulated-arm CMM 2000 . Six-DOF tracker 1000 immediately determines the six degrees-of-freedom of referenced articulated-arm CMM and converts the 3D coordinates measured by referenced articulated-arm CMM into the global frame-of-reference.
- Camera internals 900 may comprise filter 914 , beam splitter 916 , right-angle reflector 917 , apertures 920 A, 920 B, cylindrical lenses 930 A, 930 B, and photosensitive arrays 940 A, 940 B.
- Filter 914 removes unwanted wavelengths of light to improve signal-to-noise ratio.
- Some light from source 902 travels through filter 914 , beamsplitter 916 , aperture 920 A, and cylindrical lens 930 A to form line of light 954 A on photosensitive array 940 A. Another part of the light travels through filter 914 , is reflected by beamsplitter 916 , reflected a second time by right-angle reflector 917 , passes through aperture 920 B and cylindrical lens 930 B to form line of light 954 B on photosensitive array 940 B.
- Cylindrical lens 930 A, 930 B may comprise multiple lens elements. Apertures 920 A, 920 B may be on either side or within the lens elements of cylindrical lens 930 A and 930 B.
- the position of the line of light on photosensitive array 940 A indicates the ratio of the y coordinate of the point of light to the z coordinate of the point of light.
- the position of the line of light on photosensitive array 940 B indicates the ratio of the x coordinate of the point of light to the z coordinate of the point of light.
- FIG. 9 the internals of another possible embodiment of camera 140 of FIG. 1 are described. It shows an imaging block within the cameras wherein the images are formed with spherical optics and an area photosensitive array.
- Camera 1100 is an embodiment of camera 140 .
- Camera 1100 comprises filter 1114 , aperture 1120 , lens 1130 , and photosensitive array 1140 .
- Source of light 1102 can be any light on a target—for example, points of light 210 , 211 , or 212 .
- Light passes through aperture 1120 , lens 1130 and comes to a small spot at point 1153 on photosensitive array 1140 . In most cases, there will be at least three image spots on photosensitive array 1140 from a corresponding number of light sources.
- Lens 1130 may comprise multiple lens elements.
- Aperture 1120 may be on either side or within the lens elements of lens 1130 .
- Camera 2100 is another embodiment of camera 140 .
- Camera 2100 comprises beam splitter 2110 , mirrors 2112 , 2114 , 2116 , 2118 spherical lenses 2122 , 2124 , and photosensitive arrays 2132 , 2134 .
- Light 2140 from a point source strikes beam splitter 2110 .
- Part of the light is reflected by the beam splitter 2110 , further reflected by mirror 2112 , and imaged by spherical lens 2122 onto photosensitive array 2132 .
- Another part of the light is transmitted through beam splitter 2110 , focused by spherical lens 2124 , reflected off mirrors 2114 , 2116 , 2118 and strikes photosensitive array 2134 .
- the focal length of lens 2124 is approximately four times as large as the focal length of lens 2122 .
- the advantage of camera 2100 is that it permits the camera to retain high accuracy over a wide range of distances while retaining a reasonably small target size.
- the focal length of lens 2122 is 150 mm and the focal length of lens 2124 is 600 mm.
- the pixels must fill anywhere from 50 to 100 percent of the edge-to-edge distance, it follows that the point sources of light located on the periphery of a 50-mm target can cover the range from 1.5 to 3 meters. If target 1200 is used, then the two concentric circles of lights permits the camera to be used over the extended range of 0.75 to 3 meters. Since lens 2124 has four times the focal length of lens 2122 , it follows that its acceptable range of distances are increased by a factor of four, which means camera 2100 can cover the range from 0.75 to 12 meters with a two-inch target. By adding to target 1200 an additional circle of lights having a diameter of 100 mm, the range can be extended to 24 meters. Cameras that can measure to such large distances need point sources of light that emit more optical power than cameras that measure to nearer distances.
- the tracker has three modes of positioning the camera: tracking mode, user-specified positioning mode, and manual positioning mode.
- tracking mode When tracking mode is turned on, the gimbal mechanism causes the camera to rotate about two axes to follow the movement of the target.
- the tracking mechanism attempts to keep a pre-defined light source, usually a central light source such as 211 or 243 , approximately centered on the photosensitive array. It is not essential that the central light source be exactly centered on the photosensitive array. It is just important that the target be centered well enough to keep the important points of light on the photosensitive array.
- the method used by the tracker to keep the central light source on the target approximately centered in the camera is as follows.
- Camera 140 sends the centroid positions of the spots of light on the photosensitive array to processor 150 .
- Processor 150 calculates the number of pixels from the centroid of the central spot of light to the effective center of the photosensitive array.
- the effective center is defined as that position where the optical axis intersects the photosensitive array.
- Processor 150 uses this number of pixels, along with the angles reported by angle meters 122 and 132 to calculate by what angles first-angle shaft (not shown) and second-angle shaft (not shown) need to be rotated to move the central spot into the effective center of the photosensitive array.
- the advantage of the tracking mode is that a user can move a target from point to point.
- the tracker will automatically follow the target without the user having to walk back to 6-DOF tracker 1000 or computer 300 to get the camera pointed in the proper direction.
- This is particularly useful when the operator is moving a target such as probe 500 , fiducial target 600 , or spherical target 700 from point to point as a way of measuring the characteristics of the part or fixture under observation.
- tracking mode is active, a large amount of data is rapidly collected and then automatically analyzed to determine characteristics such as surface contour, hole or feature position, hole, sphere, or cylinder diameter, surface flatness, perpendicularly between adjacent surfaces, departure of surfaces from CAD specifications, and so forth.
- a second mode is user-specified positioning mode.
- the user specifies the approximate coordinates of the target or, alternatively, the direction in which the camera is to be pointed.
- the “user” is actually computer 300 , which has been programmed to measure at predetermined coordinates.
- One example of a useful application for user-specified positioning mode is to move the camera appropriately to accurately measure the position of a robot end effector. The end effector has been approximately placed in the predetermined position by the robot itself, which makes it easy for computer 300 to drive the camera.
- Another example of a useful application for user-positioning mode is to measure a number of fiducial targets ( 600 ) or repeatability targets (not shown).
- Fiducial targets are similar to fiducial targets except that repeatability targets are typically glued to surfaces rather than placed in holes or nests. Fiducial targets are often measured to quickly establish a frame of reference for the fixture or part under test. Both fiducial and repeatability targets are often used to verify thermal and mechanical stability of a tool, fixture, or part.
- a third mode is manual positioning mode.
- motors 124 and 134 are turned off and the user physically points the camera in the desired direction. With the camera pointed in approximately the right direction, the motors are turned on. If the target is within view of the camera, motors 124 and 134 quickly center the target in the camera. If the target points of light are out of view, a search procedure is carried out in which motors 124 and 134 move the camera in a pattern such as a spiral until the points of light are found.
- Manual positioning mode is often convenient when tracking has been lost and the nominal coordinates of the target are not known.
- the orientation of target 400 for example is known ahead of time.
- the position of the target such as target 500 , 600 , 700 , or 1200 may not be known ahead of time, and there may be a 180-degree ambiguity in the orientation of the target.
- light sources 211 and 212 could be flashed at the start of a measurement while light source 210 was left off. This removes the 180-degree ambiguity and establishes the identity of the light sources on the target.
- a target 200 A there are three points of light 210 , 211 , and 212 on a target 200 A and another point such as the tip of tool 412 , whose position we would like to know, which is fixed relative to the target.
- This point may be the tip of a drill bit attached to a robot arm or the tip of a handheld probe.
- the point may also be the center of a spherical target, the center of a hole beneath a fiducial target, or a variety of other locations.
- the rotating camera 140 frame of reference have as its origin the intersection of the optical axis 1112 and the entrance pupil of the camera lens 1130 for example when using the spherical lens 1130 camera shown in FIG. 5 .
- the entrance pupil is defined as apparent aperture-stop as viewed from the front of the lens 1130 . If aperture 1120 is in front of lens 1130 , then the entrance pupil will coincide with aperture 1120 . From the equations of paraxial (small angle) optics, all rays appear to converge to the entrance pupil. In reality, this is not quite true, and we must make a correction to account for the departure from paraxial conditions. This is explained below.
- This correction value is determined at the factory by taking a number of measurements.
- the correction values can be efficiently described as polynomial expansions in odd powers of the field angle.
- first axis 126 is the zenith (y) axis and second axis 136 is the azimuth (z) axis.
- the zenith and azimuth axes coincide at a common point, called the gimbal point.
- the optical axis of the camera passes approximately through the gimbal point.
- a rotation matrix is derived by performing Euler angle rotations in this order: z-axis, y-axis, and x-axis.
- angles of rotation about the z-axis, (rotated) y-axis, and (rotated) x-axis be rz, ry, and rx, respectively.
- the angles ry and rz are determined by the readings of the angle meters 122 and 132 .
- the angle rz is a constant value determined by the orientation of the photosensitive array relative to the other two axes.
- the center of the lens entrance pupil be the origin of the rotating camera and let the gimbal point be the origin of the fixed tracker. The coordinates of the tracker origin relative to the camera origin are then (tx, ty, tz).
- the three-dimensional coordinates of the three or more points of light on the target are known.
- the usual objective is to find the position of another point, such as a probe tip or a drill bit, that is rigidly affixed to the target.
- To find the position of this point in the tracker frame of reference it is necessary to know the position of this point relative to the other points of light on the target.
- a way to do this is to establish a target frame of reference by letting points of light 210 and 212 represent the y axis and point of light 211 through pedestal 220 represent the z axis.
- the point to be determined corresponds to a probe tip such as tip 530
- factory procedures are performed ahead of time to find the coordinates in the target frame of reference.
- To find the coordinates of probe tip 530 in the fixed-tracker frame of reference it is necessary to determine a transformation matrix similar to the one in Equation (4).
- This transformation matrix is found from the coordinates of the three or more points of light on the target, relative to the fixed-tracker frame of reference, using traditional methods of linear algebra. Because these methods are well known, they are not be discussed further.
- the point to be determined is the tip of a tool 412
- the coordinates of the tool tip cannot be determined at the factory but must be determined by an on-site procedure.
- One possible on-site procedure is to move the tool tip to a particular position and then measure that position using probe 500 or similar means.
- the tool may be used to perform an action, such as drilling a hole and then measuring the characteristics (position and depth) of that hole using probe 500 or similar means.
- the same linear algebra methods which are well known to those skilled in the art, are used to determine the transformation matrix for this case.
- a correctly designed system has accuracy of approximately 10 ppm in both radial and angular measurement, which is comparable to that obtained by the laser tracker, generally regarded as the most accurate large-scale portable coordinate measuring instrument available today.
- a question that might arise is what is meant by terms such as “a narrow field or view” and “nearly filling the photosensitive array,” which have been used here.
- the radial accuracy in this case is approximately 5 ppm and the angular accuracy, which is dominated by the accuracy of the angular encoders, is approximately 10 ppm. If this same target is moved 2 meters from the camera, the radial accuracy will drop to 10 ppm, and the angular accuracy will remain nearly unchanged at approximately 10 ppm. If this same target is moved farther away from the same tracker, then the relative uncertainty in the radial measurement will increase while the relative uncertainty in the angular measurement will still be approximately 10 ppm. To get around this increase in the relative uncertainty of radial measurements, targets like 200 B can be used.
- the target length would have to be increased from 50 mm to 100 mm to maintain an accuracy of 10 ppm out to 4 meters and to 200 mm to maintain an accuracy of 10 ppm to 8 meters.
- radial distance accuracy of measurements made with single cameras has not been considered good enough for metrology-grade measurements.
- high accuracy measurements can be obtained in at least one embodiment herein from a single camera if the following preferable conditions are met:
- the camera has a narrow field of view so that the photosensitive array corresponds to only a small angular region; the image extends over a large fraction of the pixels on the photosensitive array; the camera has 100% fill factor and at least 1000 pixels along each dimension; the camera lens is of good quality and coatings are provided to block out unwanted wavelengths of light; and compensation is applied to remove aberrations in the camera system.
- other variations and arrangements are also possible and are within the scope of the present invention.
- N T be the number of pixels along one dimension in photosensitive array 1140 for example and N be the maximum number of pixels between any two spots of light on the image of photosensitive array 1140 .
- R be the average distance from the lens 1120 to the target points of light, and let R 0 be the distance from lens 1120 to the position at which the outermost image spots are at opposite edges of the array. The following formula holds:
- Equation (10) indicates that the relative uncertainty is proportional to radial distance. This behavior is not found in most other measuring devices such as angular encoders, interferometers, or high performance absolute distance meters, which have relative error that is constant and independent of distance.
- the subpixel accuracy for a single point of light is one part in 100 or better.
- two pixels are measured, and each contributes its own random noise.
- the resulting noise is then 1 part in 70.7.
- Equation (10) above has been thoroughly tested using Monte Carlo simulation and found to hold under a wide range of conditions.
- the target can be rotated into a variety of angles. These angles can be described as rotations about the three axes: ⁇ x , ⁇ y , and ⁇ z . Sometimes the terms pitch, yaw, and roll are alternatively used to describe three orthogonal rotations. Here the z axis corresponds to the optical axis of the camera. The accuracy of these three angles affects mostly the accuracy of a point which is attached to the target—for example, the tip of a probe or tool.
- target 200 A having three points ( 210 , 211 , and 212 ) located at (0, 0, 0), (a, 0, b), and ( ⁇ a, 0, b).
- the three points appear to form a straight line, with one point midway between the other two.
- the x-axis is rotated by an angle ⁇ x about the origin point (0, 0, 0).
- the other two points rotate to coordinates (a, ⁇ b sin ⁇ x ,b cos ⁇ x ) and ( ⁇ a, ⁇ b sin ⁇ x ,b cos ⁇ x ).
- the uncertainty in the orientation (pitch, roll, and yaw) angles is multiplied by the distance from the origin of target to the point that is to be determined, which might be the tip of a probe or the tip of a tool such as a drill. For example, if a drill tip is located on an end effector 400 at a distance 200 mm below the center of target 200 B, the uncertainty in the position of the drill tip in relation to the target is approximately 14 ppm multiplied by 0.2 meter, which is 2.8 micrometers.
- a convenient method for determining the x-y-z coordinates of a machine tool, probe tip, or fiducial marker is to determine the coordinates of the target point relative to an arbitrary origin point. A best-fit calculation is then carried out to determine the distance to the origin point and the three rotation angles ⁇ x , ⁇ y , and ⁇ z . Finally, this information is used to calculate the position of the machine tool, probe tip, or fiducial marker.
- an angular correction is added to the angles indicated by angle meters 122 and 132 , which are preferably angular encoders.
- This angular correction is based on the image pattern at the camera array.
- the uncertainty in this angular correction is ( ⁇ FOV /N T )dN.
- the uncertainty in the correction value is 0.35 microradian, which is a very small uncertainty.
- the uncertainty in the angular measurement of a gimbal system includes uncertainty components from the angular encoders, bearings, kinematic compensation, and angular correction as described above.
- the total angular error of 5 to 10 microradians is possible. This is equivalent to saying that the accuracy of the angular encoder is 5 to 10 ⁇ m/m or 5 to 10 ppm. Under these conditions, the angular correction component of the angular uncertainty is negligible.
- Kinematic uncertainty refers to uncertainty associated with kinematic parameters such as R0 (distance from gimbal point to reference point on the instrument), Axis Offset (distance between mechanical axes at the point of closest approach), Axis Non-squareness (angle between the two mechanical axes with respect to 90 degrees), and so forth.
- the uncertainty components are approximately (1) 7-14 ppm in radial distance, (2) 5-10 ppm in side-to-side (angular) distance, and (3) 1-2 ppm in kinematic effects.
- the uncertainty in the relative tip position is approximately 14 ppm, but this value is multiplied by the distance from the target to the probe tip rather than by the distance from the target to the tracker. For this reason, the uncertainty in the relative tip position is usually small and can be ignored.
- Radial and angular uncertainties are approximately equal, which will result in an uncertainty region in space that is approximately spherical and about 7-14 ppm in radius.
- this relative uncertainty is converted into an absolute uncertainty
- a target is measured at 3 meters with a relative uncertainty of 10 ppm.
- an uncertainty of 150-200 micrometers is considered adequate in most cases.
- the device described here therefore has the accuracy required for this application.
- the simplicity of the design makes a low-cost, metrology-grade instrument available for the first time.
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Abstract
Description
- This application claims priority to U.S. provisional application, 60/793,487, filed Apr. 20, 2006, the entire contents of which are incorporated herein by reference.
- The present disclosure relates to a coordinate measuring device. One set of coordinate measurement devices belongs to a class of instruments that measure the three-dimensional coordinates of a point by sending a laser beam to the point. The laser beam may impinge directly on the point or may impinge on a retroreflector target that is in contact with the point. In either case, the instrument determines the coordinates of the point by measuring the distance and the two angles to the target. The distance is measured with a distance-measuring device such as an absolute distance meter or an interferometer. The angles are measured with an angle-measuring device such as an angular encoder. A gimbaled beam-steering mechanism within the instrument directs the laser beam to the point of interest. Exemplary systems for determining coordinates of a point are described by U.S. Pat. No. 4,790,651 to Brown et al. and U.S. Pat. No. 4,714,339 to Lau et al.
- The laser tracker is a particular type of coordinate-measuring device that tracks the retroreflector target with one or more laser beams it emits. A coordinate-measuring device that is closely related to the laser tracker is the laser scanner. The laser scanner steps one or more laser beams to points on a diffuse surface.
- A second set of coordinate measurement devices belongs to a class of instruments that measure coordinates using one or more cameras to view points of light attached to a probe. Cameras view these points of light and from the images determine the position of the probe tip. In most cases, two or more cameras are used. These cameras may be rigidly connected, or they may be set up individually according to the particular measurement requirements. If the cameras are not rigidly connected, a reference length must be measured by the cameras either before or during the measurement to establish the scale. An exemplary system for determining the coordinates of a point using cameras and points-of-light is described by U.S. Pat. No. 5,196,900 to Pettersen.
- It is also possible to find the coordinates of a probe tip by using a single camera to view points of light attached to the probe. Generally such devices are regarded as not very accurate but appropriate when low cost or ability to see into narrow openings is important. An exemplary system for determining the coordinates of a probe tip using a single camera is described by U.S. Pat. No. 5,440,392 to Pettersen, et al.
- To get around the limitations in radial distance accuracy in the single-camera system, methods have been devised for combining a camera with a rangefinder. In one embodiment, a rangefinder comprises a distance meter and one or more steering mirrors. The rangefinder measures the distance to a retroreflector mounted on a probe. Simultaneously, a camera positioned near the rangefinder measures the angles to point light sources located on the probe. The combination of distance and angle information gives the coordinates of the probe tip. In a second embodiment, a rangefinder comprises a distance meter and one or more steering mirrors. The rangefinder directs light to a retroreflector mounted on a probe. Part of the laser light returning from the retroreflector travels to a distance meter and another part splits off to a camera. The camera also measures the angles to point light sources located on the probe. The combination of distance and angle information gives the coordinates of the probe tip. An exemplary system for determining the coordinates of a probe tip using a camera in conjunction with a rangefinder is described in U.S. Pat. No. 5,973,788 to Pettersen, et al.
- None of these coordinate measurement devices is ideal for many of the problems in an automated factory. Laser trackers, though highly accurate and fast, are too expensive for many common operations such as precisely positioning robot end effectors to drill holes. In addition, laser trackers measure only three-dimensional coordinates rather than all six degrees of freedom. Because of this, laser trackers must in some cases measure three or more targets to find all six degrees of freedom. Measuring multiple targets in this way requires additional time and targets.
- Camera-based coordinate measurement devices based on two or more cameras are also expensive and also have geometrical limitations. To be accurate, individual cameras must be spaced relatively far apart compared to the measurement range. Consequently, camera systems are limited in their ability to see into narrow openings. Camera systems also have a limited field-of-view, which means that time-consuming relocation procedures may be necessary to view all targets within the measurement volume.
- Systems that contain only a single camera can be made inexpensively but are not accurate enough in measuring radial distance when a small target appropriate for robotic control or factory automation is used. Adding a rangefinder improves accuracy but is too expensive for most robotic and factory automation applications. In view of these limitations, there is a need today for a device that is low cost and accurate and that does not have the geometrical limitations of today's camera-based systems.
- An embodiment may comprise a camera based target coordinate measuring system and/or apparatus for use in measuring the position of objects in manner that preserves a high level of accuracy. This high level of measurement accuracy is usually only associated with more expensive laser based devices. Many different arrangements are possible.
- For example, in one embodiment, a camera based target coordinate measuring system for use in measuring the position of objects without requiring use of a laser range finder for measuring distance comprises a camera rotatable about a first axis and a second axis; a target having at least three or more light sources wherein the light sources are located on the target at known three-dimensional coordinates relative to each other and wherein at least one of the light sources is located at a different distance from the camera than the midpoint of a line segment connecting two of the other light sources, and wherein the target is structured to be placed on an object to be measured or to be placed on a device to measure the object; two angular measuring devices to measure the angles of rotation of the camera about the first and second axes; at least one motor to rotate the camera about the first and second axes; a photosensitive pixel array located in the camera for recording images of the light sources on the target; and a processor for directing the motor and for determining up to three positional degrees of freedom and up to three rotational degrees of freedom of the target.
- Another embodiment may comprise a camera based coordinate measuring system for use in measuring the position of a target relative to at least one frame of reference without requiring use of a laser range finder for measuring distance comprising: at least three or more light sources located on a target at known three-dimensional coordinates relative to each other; at least one rotatable camera rotatable on about a first axis and a second axis wherein the camera records positions of the light sources; and two angular measuring devices to measure the angles of rotation of the camera about the first and second axes; and a processor for determining up to three positional degrees of freedom and up to three rotational degrees of freedom of the target.
- Other embodiments may comprise related methods of using a camera based target coordinate measuring method for use in measuring the position of objects. Many variations of the methods are possible.
- For example, one specific method comprises, a camera based target coordinate measuring method for use in measuring the position of objects without requiring use of a laser range finder for measuring distance comprising: operating a camera rotatable about a first axis and a second axis; placing a target to view with the camera and having at least three or more light sources wherein the light sources are located on the target at known three-dimensional coordinates relative to each other and wherein at least one of the light sources is located at a different distance from the camera than the midpoint of a line segment connecting two of the other light sources, and wherein the target is structured to be placed on an object to be measured or to be placed on a device to measure the object; measuring angles of rotation of the camera about the first and second axes with two angular measuring devices; rotating the camera about the first and second axes with at least one motor; recording the images of the light sources on a photosensitive pixel array located in the camera; and determining in a processor up to three positional degrees of freedom and up to three rotational degrees of freedom of the target.
- Referring now to the drawings, exemplary embodiments are shown which should not be construed to be limiting regarding the entire scope of the disclosure, and wherein the elements are numbered alike in several FIGURES:
-
FIG. 1 is a perspective view of an exemplary three-dimensional measuring device and system; and -
FIGS. 2A and 2B are perspective views ofexemplary targets -
FIGS. 3A-3F are perspective views ofexemplary targets -
FIGS. 4A and 4B are perspective and front views ofexemplary target 1200; and -
FIGS. 5A-5F are perspective views ofexemplary targets 1200; and -
FIG. 6 is a perspective view of an exemplary referenced hand-heldscanner 1800; and -
FIG. 7 is a perspective view of an exemplary referenced articulatedarm CMM 2000; and -
FIG. 8 is a perspective view of the internals of one possible embodiment ofcamera 140 with cylindrical lenses; and -
FIG. 9 is a perspective view of the internals of another possible embodiment ofcamera 140 with a spherical lens; and -
FIG. 10 is a schematic representation of another possible embodiment ofcamera 140 with spherical lens and two beam paths. - As shown in
FIG. 1 , an exemplary six degree of freedom (6-DOF)tracker 1000 may comprise arotating tracking camera 100,target 400, andcomputer 300. Six degrees of freedom may be the x, y, z coordinates, and the pitch, roll, and yaw oftarget 400 for example. - Overall tracking
camera apparatus 100 may comprise first-angle assembly 120, second-angle assembly 130,camera 140, andprocessor 150. - First-
angle assembly 120 comprises first-angle shaft (not shown) onto which are mountedangle meter 122 andmotor 124.Angle meter 122 is preferably an angular encoder andmotor 124 is preferably a servo-motor. First-angle shaft (not shown) rotates aroundfirst axis 126, which in this figure is the zenith axis. The first and second axes intersect at a point in space called the gimbal point. - Second-
angle assembly 130 comprises second-angle shaft (not shown) onto which are mountedangle meter 132 andmotor 134.Angle meter 132 is preferably an angular encoder andmotor 134 is preferably a servo-motor. Second-angle shaft (not shown) rotates aroundsecond axis 136, which in this figure is the azimuth axis. -
Camera 140 is mounted on first-angle assembly 120. First angle assembly and camera rotate aboutfirst axis 126. First angle assembly is mounted on second-angle assembly. Second-angle assembly 130 rotates with respect to the base aboutsecond axis 136. - The
camera 140 shown in theFIG. 1 is well known. All that is necessary is that it is possible to direct thecamera 140 to point at any direction within the measurement volume. Any two angular rotations can be used to obtain the desired imaging oftarget 200B on the camera. -
Targeted end effector 400 comprisesend effector 410 and one or more oftarget 200B in this example.End effector 400 may be mounted on a robot arm or machine tool for example.Tool 412, which may be a drill bit, mill, or any other attachment, is connected to endeffector 410. Many other configurations are also contemplated herein, andFIG. 1 merely shows one of many possible configurations. - The purpose of
camera 140 is to form an image oftarget 200B on a photosensitive array within the camera and to read out the values on this array for analysis so that the position oftool 412 can be precisely controlled. Of note,tool 412 can be controlled even when it is not visible tocamera 140 so long astarget 200B is visible. -
Processor 150 uses image intensity values from pixels ofcamera 140 and angle data fromangle meters target 400.Processor 150 also sends control signals tomotors - There are three types of position control that can be selected by the user: (1) tracking position control, (2) user-specified position control, and (3) manual position control. If tracking position control is selected,
processor 150 causes the motor to be adjusted to keep target 200 approximately centered on the photosensitive array(s) withincamera 140. If user-specified position control is desired,processor 150 causes motors to drive mirror to the direction selected by the user. If manual position control is desired,motors - With reference to
FIG. 2 , target 200 comprises at least three points of light at fixed positions relative to one another. In general, by using more than 3 points, it is possible to maintain high radial accuracy over an extended range. For example, target 200A, which is a first embodiment of target 200, comprises points oflight pedestal 220, andbase 230. Points of light are preferably LEDs but may be other types of active light sources or may also be passive reflectors. An example of a passively reflector is a photogrammetric spot that is illuminated by flashing lights located in the vicinity of 6-DOF tracker 1000. -
Target 200B, which is a second embodiment of target 200, comprises seven points of light 240-246, five pedestals 250-254, andbase 260. In operation, additional points of light ontarget 200B are turned on astarget 200B moves away from 6-DOF tracker 1000 withcamera 140. Thus, when thetarget 200B is located close to 6-DOF tracker 1000, points oflight light light - Ordinarily base 230 or 260 is attached to some other object whose six degrees of freedom are to be measured. Pedestals such as 220 and 250-254 provide a geometry that is favorable for high accuracy measurement of radial distance to the object. A light source is mounted onto a pedestal so that its axis of emission is approximately in line with the axis of the pedestal.
Camera 140 points at a target, which may be 200B, for example, as shown inFIG. 1 . The axis ofcamera 140 is kept more or less in line with the axes of the pedestals. A good rule of thumb is that the optical axis ofcamera 140 should be within ±45 degrees of the pedestal axes. As explained in the section on System Accuracy, the best accuracy is obtained when the angle is zero degrees. - A good choice for light sources 210-212 and 240-246 are LEDs that emit over a wide field of view. LEDs that emit over a full-angle of 110 to 120 degrees are readily available. The pedestals are preferably tall enough so that the higher pedestals do not clip the light emerging from the lower pedestals. Also the pedestals should be tall enough to provide sufficient accuracy. A good rule of thumb is that the pedestals should be tall enough to produce an angle of at least 20 degrees between
base 230 and the line oflight sources base 260 and the line of light sources 240-243. The advantage of having a large enough angle will be made clear in the section on System Accuracy. - Although
targets FIG. 2 . - Points of light 210-212 in 200A and 240-246 in 200B are coplanar and appear to form a straight line when viewed from a certain direction. This pattern was selected because its principle of operation is easy to explain. However, in general, the light sources can be arranged in a variety of patterns without sacrificing accuracy. It is not necessary that all of the points be coplanar or that they appear to form a straight line when viewed from a particular direction.
- To understand the benefit of the arrangement of light sources in
target 200B, consider the following. In general, the spots of light on the photosensitive array withincamera 140 will not fill the array. In other words, the spots of light will not extend from the far left side of the array to the far right, nor will they extend from the lower edge to the upper edge. Instead, some smaller fraction of the array is usually covered. Another way of saying this is that only a fraction of the available range of pixels along a given direction in the array is subtended by the spots of light in the image. As explained in the section on System Accuracy, the relative uncertainty in radial distance measurement of 6-DOF tracker 1000 is proportional to the fraction of the photosensitive array in the camera subtended by the points of light from thetarget 200B for example. Astarget 200B moves away from 6-DOF tracker 1000, the fraction of the array subtended by points of light decreases, causing the relative accuracy to decrease proportionately. By turning on additional points of light astarget 200B moves away from 6-DOF tracker 1000, the relative accuracy is restored. The light sources intarget 200B are spaced such that size of the target visible tocamera 140 increases by a factor of 2 each time two new spots of light appear in the camera image. - As a specific example, suppose that
LEDs target 200B is 1 meter from 6-DOF tracker 1000. Astarget 200B moves to nearly 2 meters away, the accuracy drops—for example, from 5 to 10 ppm, as explained in the section on accuracy below. As the target moves to greater than 2 meters away, points oflight light - In reference to
FIG. 3 , other embodiments of target 200 are shown. For example, targetedend effector 400 comprisesend effector 410 and one or more ofembodiment target 200B. (Target 200A could equally well have been used.)End effector 400 may be mounted on a robot arm or machine tool for example.Tool 412, which may be a drill bit, mill, or any other attachment, goes onend effector 410. - Also, for example,
probe 500 comprisesprobe body 510,shaft 520,tip 530, and one ormore targets 200A. (Target 200B or any other collection of three or more points could equally well have been used.) By analyzing the image of the points of light ontargets 200A, the 6-DOF tracker calculates the coordinates ofprobe tip 530.Probe tip 530 may be inserted inside holes or behind objects that are not visible to the camera in 6-DOF tracker 1000.Probe 500 may take any shape. The probe may be tilted in any direction or bent into any shape. Probebody 510 may be any length. - Also another embodiment of a target, for example, tooling-
hole fiducials 600 sit inside tooling holes (not shown) that have been drilled in a tool or work piece to serve as fiducial (reference) points. The purpose of tooling-hole fiducials is to enable determination of the coordinates of the tooling hole. This information may be used to establish the frame of reference of the measuring instrument in terms of the global coordinates of the tool or work piece. This information may also be used to check for changes in the work piece caused by thermal expansion or similar effects. - Tooling-hole fiducial 610 comprises
shank 612,body 614, andvertical target 200A.Shank 612 sits inside the tooling hole. Tooling-hole fiducial 620 comprisesshank 622,body 624, andhorizontal target 200A. Tooling-hole fiducial 630 compriseshemisphere 632,nest 640, and target 200C.Target 200C is liketarget 200A except that the pedestals are located beneath the outermost points intarget 200C rather than the innermost as intarget 200A. On the bottom ofnest 640 is a shank (not shown) that sits inside a tooling hole. The center point of light of target 200 is located at the spherical center ofhemisphere 632 so that its coordinates do not change ashemisphere 632 is rotated. In this embodiment for example, the purpose of having three different types of tooling-hole fiducials is to provide an appropriate viewing angle for 6-DOF tracker 1000. However, any number of tooling-hole fiducials may be used depending upon the application. -
Spherical target 700 comprisesspherical body 712 and points oflight 714 and central point oflight 716. Central point of light 716 is located at the spherical center ofspherical body 712. Asspherical body 712 is rotated, central point of light 716 remains fixed.Spherical target 700 may be moved over any object as a way of determining the coordinates of points of an entire surface or multiple surfaces. Because the distance from the spherical center and the surface being touched bytarget 700 is a known constant value, the coordinates of the surface being measured can be determined. From the collected data, characteristics of the object such as flatness, perpendicularity, diameter, and so forth can be found. Alternatively, anest 800 can be attached to the surface at various points. The nest provides a convenient alternative to tooling holes for establishing fiducial locations.Spherical target 700 has fourlight sources 714 along the upper surface ofspherical body 712. Twolight sources 714, in addition tolight source 716, are sufficient to determine the angles and distance to the center ofsphere 716. The additional two points of light 714 (four rather than two) have been added to improve accuracy. Additionally, two sources oflight 714 and one source of light 716 are sufficient to provide the pitch, roll, and yaw angles ofspherical target 700. However, because point of light 716 is located in the center of a spherical surface, pitch, roll, and yaw angles are not ordinarily required to make measurements withspherical target 700. - Referring to
FIG. 4 ,target 1200 comprisesmount 1210; pedestals 1271-1274, 1281-1284; and point sources of light 1220-1234, 1241-1244, 1251-1254, 1261-1264.Mount 1210 and pedestals 1271-1274, 1281-1284 are preferably made of a material having a low thermal coefficient of expansion such as Invar. Point sources of light 1220-1234, 1241-1244, 1251-1254, and 1261-1264 are preferably light-emitting diodes that are not covered by glass, epoxy, or similar material, unobstructed by bonding wires, and having a wide angle of emission. Alternatively, point sources of light 1220-1234, 1241-1244, 1251-1254, and 1261-1264 may be photogrammetric targets illuminated by an external source of light. Point sources of light are located either alongcircle target 1200 is relatively far from trackingcamera 100, point sources of light 1251-1254, 1261-1264 along theouter circle 1250 and point source of light 1220 are illuminated. Whentarget 1200 is too close to 6-DOF tracker 1000 for all LEDs alongouter circle 1250 to be simultaneously viewed by the photosensitive array within 6-DOF tracker 1000, then point sources of light 1231-1234, 1241-1244 along inner circle are illuminated. The additional point sources of light intarget 1200 compared totargets Target 1200 has eight point sources of light alongcircle 1230 and eight points of light alongcircle 1250. This compares to only two equivalent points intargets target 1200 is expected to be approximately two times better than that oftargets target 1200, additional circles of LEDs may be placed insidecircle 1230 or outsidecircle 1250. - In reference to
FIG. 5 , other embodiments oftarget 1200 are shown. For example, targetedend effector 1300 comprisesend effector 1310 andtarget 1200. End effector may be mounted on a robot arm or machine tool for example.Tool 1312, which may be a drill bit, mill, or any other attachment, goes onend effector 1310. - Also, for example,
probe 1400 comprisesprobe body 1410,shaft 1420,tip 1430, andtarget 1200. By analyzing the image of the points of light ontarget 1200, the 6-DOF tracker 1000 calculates the coordinates ofprobe tip 1430.Probe tip 1430 may be inserted inside holes or behind objects that are not visible to the camera in a 6-DOF tracker 1000.Probe 1400 may take any shape. The probe may be tilted in any direction or bent into any shape. Probebody 1410 may be any length. The length will be a known dimension. - Also another embodiment of a target, for example, tooling-
hole fiducials 1500 sit inside tooling holes (not shown) that have been drilled in a tool or work piece to serve as fiducial (reference) points. The purpose of tooling-hole fiducials is to enable determination of the coordinates of the tooling hole. This information may be used to establish a frame of reference of the measuring instrument in terms of the global coordinates of the tool or work piece. This information may also be used to check for changes in the work piece caused by thermal expansion or similar effects. - Tooling-hole fiducial 1510 comprises
shank 1512,body 1514, andvertical target 1200.Shank 1512 sits inside the tooling hole. Tooling-hole fiducial 1520 comprises shank 1522, body 1524, andhorizontal target 1200. Tooling-hole fiducial 1530 comprises hemisphere 1532 (hidden from view inFIG. 5E but having the same shape ashemisphere 632 inFIG. 3E ),nest 1540, andtarget 1200. On the bottom ofnest 1540 is a shank (not shown) that sits inside a tooling hole. The center point of light oftarget 1200 is located at the spherical center of hemisphere 1532 so that its coordinates do not change as hemisphere 1532 is rotated. The purpose of having three different types of tooling-hole fiducials 1500 is to provide an appropriate viewing angle for 6-DOF tracker 1000. -
Spherical target 1600 comprisesspherical body 1612 andtarget 1200. The point of light 1220 centered intarget 1200 is located at the spherical center ofspherical body 1612. Asspherical body 1612 is rotated, point of light 1220 remains fixed.Spherical target 1600 may be moved over any object as a way of determining the coordinates of points of an entire surface or multiple surfaces. Because the distance from the spherical center and the surface being touched bytarget 1600 is a known constant value, the coordinates of the surface being measured can be determined. From the collected data, characteristics of the object such as flatness, perpendicularity, diameter, and so forth can be found. Alternatively, anest 1700 can be attached to the surface at various points. The nest provides a convenient alternative to tooling holes for establishing fiducial locations. -
FIG. 6 shows another embodiment oftarget 1200. Referencedscanner 1800 comprises target(s) 1200 located on one or more faces ofhand scanner body 1810 that is attached tohand scanner grip 1820. An operator holds hand scanner grip 1920 while pointingreference scanner 1800 at object-under-inspection 1900. Referencedscanner 1800 generates laser-line 1830 that strikes object-under-inspection 1900, thereby scattering light that is picked up by electro-optic detecting components (not shown) within referenced scanner. From this detected light, referenced scanner determines the three-dimensional contour of object-under-inspection 1900 relative to its own internal frame of reference. At the same time, 6-DOF tracker 1000 measures the six degrees of freedom of referencedscanner 1800 and uses this information to transform the scanned data into the global frame of reference. In this way, the operator can move referencedscanner 1800 to any location within the range of rotation of 6-DOF tracker 1000. The result is a contour of the entire object-under-inspection 1900 within the global frame-of-reference. - An alternative to mounting targets 1200 (or other targets such as 200A, 200B, or 200C) onto
hand scanner body 1810 is to build the mounts for the point sources of light directly intohand scanner body 1810. For example, hand scanner body can be molded of carbon fiber composite, thereby achieving a stable mount with a very low coefficient of thermal expansion (CTE) for relatively low cost. This method also permits reinforcement that protects the protruding point sources of light. - Although specific locations are given in
targets hand scanner body 1810 and that the arrangements described here are not to be construed as limiting to the design. - A variant of the hand scanner shown in
FIG. 6 is a scanner like that shown inFIG. 6 but mounted on a robotic structure (that is not held by hand). The robotic structure may be one that has many degrees of freedom, and in this case the scanner is mounted on the robot end effector. Alternatively, the scanner may be mounted on a robotic structure that moves rectilinearly. This rectilinear structure may be a simple motorized rail that moves in one dimension or a gantry structure that moves in two or three dimensions. Whether the movement of the robotic structure has numerous degrees of freedom or is constrained to rectilinear movement, points of light are mounted on the robotic structure in such a way as to permit inspection data collected by the scanner to be transformed into the global frame of reference.FIG. 6 shows an exemplary method of mounting the points of light onto the scanner that is attached to a robotic structure. In this case, however,grip 1820 would be removed andtargets 1200 would be attached directly to the robotic structure. -
FIG. 7 shows another embodiment oftarget 1200. Referenced articulated-arm coordinate measuring machine (CMM) 2000 comprises articulated-arm CMM 2010 andtarget 1200. Articulated-arm CMM 2010 comprisesstationary base 2012, a plurality ofrotatable segments 2014A-2014F,probe tip 2016, and angular encoders 2018 (internal components that are not visible inFIG. 7 ). The operator bringsprobe tip 2016 into contact with the object-under-inspection (not shown). Angular encoders 2018 are located at each joint. They measure the angles ofrotatable segments 2014A-2014F, and these angles are used to calculate the position ofprobe tip 2016 to high accuracy. Each articulated-arm CMM 2010 has a certain maximum reach that is determined by the combined length of the individual rotatable segments. To measure large objects-under-inspection, it is necessary to move articulated-arm CMM 2010 to multiple locations. Traditional methods for doing this such as measuring multiple target nests in a piggyback fashion can be time consuming and inconvenient. This problem is eliminated when 6-DOF tracker 1000 images light emitted bytarget 1200 in referenced articulated-arm CMM 2000. Six-DOF tracker 1000 immediately determines the six degrees-of-freedom of referenced articulated-arm CMM and converts the 3D coordinates measured by referenced articulated-arm CMM into the global frame-of-reference. - Referring to
FIG. 8 , the internals of a possible embodiment ofcamera 140 ofFIG. 1 are described.Camera internals 900 may comprisefilter 914,beam splitter 916, right-angle reflector 917,apertures cylindrical lenses photosensitive arrays point 902. This may correspond to any light found on targets—for example, 210, 211, or 212.Filter 914 removes unwanted wavelengths of light to improve signal-to-noise ratio. Some light fromsource 902 travels throughfilter 914,beamsplitter 916,aperture 920A, andcylindrical lens 930A to form line of light 954A onphotosensitive array 940A. Another part of the light travels throughfilter 914, is reflected bybeamsplitter 916, reflected a second time by right-angle reflector 917, passes throughaperture 920B andcylindrical lens 930B to form line of light 954B onphotosensitive array 940B.Cylindrical lens Apertures cylindrical lens - The position of the line of light on
photosensitive array 940A indicates the ratio of the y coordinate of the point of light to the z coordinate of the point of light. Similarly the position of the line of light onphotosensitive array 940B indicates the ratio of the x coordinate of the point of light to the z coordinate of the point of light. - In reference to
FIG. 9 , the internals of another possible embodiment ofcamera 140 ofFIG. 1 are described. It shows an imaging block within the cameras wherein the images are formed with spherical optics and an area photosensitive array. -
Camera 1100 is an embodiment ofcamera 140.Camera 1100 comprisesfilter 1114,aperture 1120,lens 1130, andphotosensitive array 1140. Source of light 1102 can be any light on a target—for example, points oflight aperture 1120,lens 1130 and comes to a small spot atpoint 1153 onphotosensitive array 1140. In most cases, there will be at least three image spots onphotosensitive array 1140 from a corresponding number of light sources.Lens 1130 may comprise multiple lens elements.Aperture 1120 may be on either side or within the lens elements oflens 1130. -
Camera 2100 is another embodiment ofcamera 140.Camera 2100 comprisesbeam splitter 2110, mirrors 2112, 2114, 2116, 2118spherical lenses photosensitive arrays Light 2140 from a point source strikesbeam splitter 2110. Part of the light is reflected by thebeam splitter 2110, further reflected bymirror 2112, and imaged byspherical lens 2122 ontophotosensitive array 2132. Another part of the light is transmitted throughbeam splitter 2110, focused byspherical lens 2124, reflected offmirrors photosensitive array 2134. For the specific layout shown inFIG. 10 , the focal length oflens 2124 is approximately four times as large as the focal length oflens 2122. - The advantage of
camera 2100 is that it permits the camera to retain high accuracy over a wide range of distances while retaining a reasonably small target size. For example, suppose that the focal length oflens 2122 is 150 mm and the focal length oflens 2124 is 600 mm. Also suppose that the photosensitive array has 1000 pixels, each 5 micrometers in length and width. If the target is 50 mm in diameter, then the image fills the photosensitive array from edge to edge when the distance from the target to the camera origin forlens 2122 is 1.5 meters. To see this, note that the distance is found by taking the target diameter times the focal length divided by the width of the photosensitive array; in other words, (50 mm)(150 mm)/(5 mm)=1.5 meters. Since the pixels must fill anywhere from 50 to 100 percent of the edge-to-edge distance, it follows that the point sources of light located on the periphery of a 50-mm target can cover the range from 1.5 to 3 meters. Iftarget 1200 is used, then the two concentric circles of lights permits the camera to be used over the extended range of 0.75 to 3 meters. Sincelens 2124 has four times the focal length oflens 2122, it follows that its acceptable range of distances are increased by a factor of four, which meanscamera 2100 can cover the range from 0.75 to 12 meters with a two-inch target. By adding to target 1200 an additional circle of lights having a diameter of 100 mm, the range can be extended to 24 meters. Cameras that can measure to such large distances need point sources of light that emit more optical power than cameras that measure to nearer distances. - As discussed previously, the tracker has three modes of positioning the camera: tracking mode, user-specified positioning mode, and manual positioning mode. When tracking mode is turned on, the gimbal mechanism causes the camera to rotate about two axes to follow the movement of the target. The tracking mechanism attempts to keep a pre-defined light source, usually a central light source such as 211 or 243, approximately centered on the photosensitive array. It is not essential that the central light source be exactly centered on the photosensitive array. It is just important that the target be centered well enough to keep the important points of light on the photosensitive array.
- The method used by the tracker to keep the central light source on the target approximately centered in the camera is as follows.
Camera 140 sends the centroid positions of the spots of light on the photosensitive array toprocessor 150.Processor 150 calculates the number of pixels from the centroid of the central spot of light to the effective center of the photosensitive array. The effective center is defined as that position where the optical axis intersects the photosensitive array.Processor 150 uses this number of pixels, along with the angles reported byangle meters - The advantage of the tracking mode is that a user can move a target from point to point. The tracker will automatically follow the target without the user having to walk back to 6-
DOF tracker 1000 orcomputer 300 to get the camera pointed in the proper direction. This is particularly useful when the operator is moving a target such asprobe 500,fiducial target 600, orspherical target 700 from point to point as a way of measuring the characteristics of the part or fixture under observation. When tracking mode is active, a large amount of data is rapidly collected and then automatically analyzed to determine characteristics such as surface contour, hole or feature position, hole, sphere, or cylinder diameter, surface flatness, perpendicularly between adjacent surfaces, departure of surfaces from CAD specifications, and so forth. - A second mode is user-specified positioning mode. In this mode, the user specifies the approximate coordinates of the target or, alternatively, the direction in which the camera is to be pointed. In most cases, the “user” is actually
computer 300, which has been programmed to measure at predetermined coordinates. One example of a useful application for user-specified positioning mode is to move the camera appropriately to accurately measure the position of a robot end effector. The end effector has been approximately placed in the predetermined position by the robot itself, which makes it easy forcomputer 300 to drive the camera. Another example of a useful application for user-positioning mode is to measure a number of fiducial targets (600) or repeatability targets (not shown). Repeatability targets are similar to fiducial targets except that repeatability targets are typically glued to surfaces rather than placed in holes or nests. Fiducial targets are often measured to quickly establish a frame of reference for the fixture or part under test. Both fiducial and repeatability targets are often used to verify thermal and mechanical stability of a tool, fixture, or part. - A third mode is manual positioning mode. In this mode,
motors motors motors - In applications such as robotic control, the orientation of
target 400 for example is known ahead of time. In other cases, such as measurement of arbitrary surfaces with the target held in the hand of the user, the position of the target such astarget light sources light source 210 was left off. This removes the 180-degree ambiguity and establishes the identity of the light sources on the target. - This is the mathematical method for the case of the rotating camera.
- Suppose that there are three points of
light target 200A and another point such as the tip oftool 412, whose position we would like to know, which is fixed relative to the target. This point may be the tip of a drill bit attached to a robot arm or the tip of a handheld probe. The point may also be the center of a spherical target, the center of a hole beneath a fiducial target, or a variety of other locations. - Let the rotating
camera 140 frame of reference have as its origin the intersection of theoptical axis 1112 and the entrance pupil of thecamera lens 1130 for example when using thespherical lens 1130 camera shown inFIG. 5 . The entrance pupil is defined as apparent aperture-stop as viewed from the front of thelens 1130. Ifaperture 1120 is in front oflens 1130, then the entrance pupil will coincide withaperture 1120. From the equations of paraxial (small angle) optics, all rays appear to converge to the entrance pupil. In reality, this is not quite true, and we must make a correction to account for the departure from paraxial conditions. This is explained below. - Let the coordinates of the three points of light (210, 211, 212) on the
target 200A relative to the rotating (camera) frame of reference be (X1, Y1, Z1), (X2 , Y2, Z2), and (X3, Y3 , Z3 ). Let the distance between the pairs of points be L12, L23, and L13. - We calculate the centroids of the three spots of light on the photosensitive array of the camera. Next, we apply a compensation correction value that is a function of the field angle and distance to the point of light relative to the camera origin.
- This correction value is determined at the factory by taking a number of measurements. Generally for symmetric lenses, the correction values can be efficiently described as polynomial expansions in odd powers of the field angle.
- After this correction has been made, the resulting coordinates of the three spots of light (210, 211, 212) on the
photosensitive array 1140 are given in the rotating (camera) frame of reference by (x1,y1), (x2 ,y2), and (x3,y3). There are now 9 unknown coordinate values {Xi,Yi,Z1}, i=1,2,3. These can be solved with 9 equations. - If ƒ is the effective focal length of the lens and if the optical axis intersects the photosensitive array at (x0, y0), then the 9 equations are:
-
x i −x 0 =−ƒ X i /Z i , i=1,2,3 (1) -
y i −y 0 =−ƒ Y i /Z i , i=1,2,3 (2) -
(X i −X j)2+(Y i −Y j)2+(Z i +Z j)2=Lij , i<j (3) - These nine equations can be solved with standard methods in linear algebra. If multiple measurements are made of the three points, then standard mathematical methods can be used to find the values for the coordinates of the points of light that give the least squared residual error. The method of minimizing the least squared residual error will also be used if a target contains more than three points of light.
- To convert from the rotating-camera frame of reference to the fixed-tracker frame of reference, we use a transformation matrix. To make the method clear, consider the specific case in which
first axis 126 is the zenith (y) axis andsecond axis 136 is the azimuth (z) axis. The zenith and azimuth axes coincide at a common point, called the gimbal point. The optical axis of the camera passes approximately through the gimbal point. To transform from the rotating-camera frame of reference to the fixed-tracker frame of reference, a rotation matrix is derived by performing Euler angle rotations in this order: z-axis, y-axis, and x-axis. Let the angles of rotation about the z-axis, (rotated) y-axis, and (rotated) x-axis be rz, ry, and rx, respectively. The angles ry and rz are determined by the readings of theangle meters -
- Let the coordinates in the fixed-tracker frame of reference be (X1T,Y1T,Z1T),(X2T,Y2T,Z2T), and (X3T,Y3T,Z3T). Define the matrices VT and V as
-
- The coordinates of the three target points of light in the fixed-tracker frame of reference are then found with this equation:
-
V T =TV (7) - Following this calculation, the three-dimensional coordinates of the three or more points of light on the target are known. As mentioned in the opening paragraph of this section, the usual objective is to find the position of another point, such as a probe tip or a drill bit, that is rigidly affixed to the target. To find the position of this point in the tracker frame of reference, it is necessary to know the position of this point relative to the other points of light on the target. A way to do this is to establish a target frame of reference by letting points of
light pedestal 220 represent the z axis. If the point to be determined corresponds to a probe tip such astip 530, then factory procedures are performed ahead of time to find the coordinates in the target frame of reference. To find the coordinates ofprobe tip 530 in the fixed-tracker frame of reference, it is necessary to determine a transformation matrix similar to the one in Equation (4). This transformation matrix is found from the coordinates of the three or more points of light on the target, relative to the fixed-tracker frame of reference, using traditional methods of linear algebra. Because these methods are well known, they are not be discussed further. For the case in which the point to be determined is the tip of atool 412, then the coordinates of the tool tip cannot be determined at the factory but must be determined by an on-site procedure. One possible on-site procedure is to move the tool tip to a particular position and then measure thatposition using probe 500 or similar means. Alternatively, the tool may be used to perform an action, such as drilling a hole and then measuring the characteristics (position and depth) of thathole using probe 500 or similar means. The same linear algebra methods, which are well known to those skilled in the art, are used to determine the transformation matrix for this case. - In the past, getting high accuracy in both radial and angular measurements with camera-based metrology systems has meant using two or more cameras spaced relatively far apart. By narrowing the field of view and ensuring that the target nearly fills the photosensitive array, we get around the accuracy problem using a single camera. This is made possible by using a gimbaled beam-steering mechanism together with angle meters such as high accuracy angular encoders. Furthermore, the gimbal/encoder arrangement can measure over a much wider range of angles than traditional multi-camera systems while also being able to see into narrow openings that are inaccessible to multi-camera systems.
- As shown below, achieving narrow field of view and ensuring that the target nearly fills the photosensitive array are important both for radial and angular accuracy. A correctly designed system has accuracy of approximately 10 ppm in both radial and angular measurement, which is comparable to that obtained by the laser tracker, generally regarded as the most accurate large-scale portable coordinate measuring instrument available today.
- A question that might arise is what is meant by terms such as “a narrow field or view” and “nearly filling the photosensitive array,” which have been used here. In the examples below, it is assumed that a photosensitive array is 5 mm on a side and has 1000×1000 pixels. If the distance from the lens to the photosensitive array of
camera 140 is 100 mm, then the angular field of view is 5 mm/100 mm=0.05 radian, which is approximately 3 degrees. If the target is 50 mm in length, then the pixels will completely cover the photosensitive array along a linear dimension such as side-to-side or up-to-down when the target is 1 meter from the camera. As indicated in the discussion below, the radial accuracy in this case is approximately 5 ppm and the angular accuracy, which is dominated by the accuracy of the angular encoders, is approximately 10 ppm. If this same target is moved 2 meters from the camera, the radial accuracy will drop to 10 ppm, and the angular accuracy will remain nearly unchanged at approximately 10 ppm. If this same target is moved farther away from the same tracker, then the relative uncertainty in the radial measurement will increase while the relative uncertainty in the angular measurement will still be approximately 10 ppm. To get around this increase in the relative uncertainty of radial measurements, targets like 200B can be used. With this type of target, additional light sources are visible as distance from tracker to target is increased, thereby restoring the radial accuracy, as explained in detail elsewhere. For the case considered here, the target length would have to be increased from 50 mm to 100 mm to maintain an accuracy of 10 ppm out to 4 meters and to 200 mm to maintain an accuracy of 10 ppm to 8 meters. A way to preserve high accuracy while using small targets is to increase the distance from the lens to the photosensitive array in the camera. For example, by increasing the distance from the lens to the photosensitive array from 100 mm to 400 mm, an accuracy of 10 ppm can be achieved to 8 meters using a target that is only 50 mm in length. In this case, the field of view is reduced to 5 mm/400 mm=0.0125 radian, which is approximately 0.7 degree. - Generally radial distance accuracy of measurements made with single cameras has not been considered good enough for metrology-grade measurements. However, high accuracy measurements can be obtained in at least one embodiment herein from a single camera if the following preferable conditions are met: The camera has a narrow field of view so that the photosensitive array corresponds to only a small angular region; the image extends over a large fraction of the pixels on the photosensitive array; the camera has 100% fill factor and at least 1000 pixels along each dimension; the camera lens is of good quality and coatings are provided to block out unwanted wavelengths of light; and compensation is applied to remove aberrations in the camera system. However, other variations and arrangements are also possible and are within the scope of the present invention.
- To obtain a large field-of-view with the narrow field-of-view camera, rotate the camera to any desired angle while simultaneously measuring the desired angle to high accuracy. Under these conditions, radial distance accuracy can be very good.
- Let NT be the number of pixels along one dimension in
photosensitive array 1140 for example and N be the maximum number of pixels between any two spots of light on the image ofphotosensitive array 1140. Let R be the average distance from thelens 1120 to the target points of light, and let R0 be the distance fromlens 1120 to the position at which the outermost image spots are at opposite edges of the array. The following formula holds: -
R=R 0 N T /N (8) -
-
- Equation (10) indicates that the relative uncertainty is proportional to radial distance. This behavior is not found in most other measuring devices such as angular encoders, interferometers, or high performance absolute distance meters, which have relative error that is constant and independent of distance.
- In a high quality camera system, the subpixel accuracy for a single point of light is one part in 100 or better. To determine a distance, two pixels are measured, and each contributes its own random noise. The resulting noise is then 1 part in 70.7. If
target 1200 or similar is used, there are four times as many point sources of light (in addition to the central point of light). This causes a reduction in the uncertainty of approximately √{square root over (4)}=2. The effective uncertainty in pixel position is then dN= 1/141. If the target image subtends all 1000 pixels in a 1000 pixel CCD array when R0=1 meter, then the total uncertainty in the radial distance measurement when the target is 1 meter from the lens is -
- The relative uncertainty is 7 μm/1 m=7 ppm. This result can also be obtained from Eq. (10). Now suppose that
target 1200 achieved the above result by using points of light located along theinner circle 1230. Iftarget 1200 is now moved to a distance 2 meters from 6-DOF tracker 1000, then the points of light alongouter circle 1250 turn on, and the relative accuracy of 7 ppm is retained. Iftarget 1200 is moved 4 meters from 6-DOF tracker 1000, then the accuracy will decrease to 14 ppm. - For the case in which measurements are being made at a stationary point, it is possible to improve accuracy by measuring the same point multiple times with the camera shifted slightly. This is called the “camera shift” technique. Since the pixel errors are random, the error in the measurement will decrease by a factor of the square root of the number of measurements, at least for a small number of measurements. For example, it is possible to move the tracker to four slightly different positions within a one or two second interval and measure the target with 6-
DOF tracker 1000 in each case. For the example given above, the uncertainty of 14 ppm at 4 meters would be reduced by the √{square root over (4)}=2 for an accuracy of 7 ppm. - Equation (10) above has been thoroughly tested using Monte Carlo simulation and found to hold under a wide range of conditions.
- The target can be rotated into a variety of angles. These angles can be described as rotations about the three axes: θx, θy, and θz. Sometimes the terms pitch, yaw, and roll are alternatively used to describe three orthogonal rotations. Here the z axis corresponds to the optical axis of the camera. The accuracy of these three angles affects mostly the accuracy of a point which is attached to the target—for example, the tip of a probe or tool.
- To calculate the uncertainty in the orientation angles for a specific case, we consider
target 200A having three points (210, 211, and 212) located at (0, 0, 0), (a, 0, b), and (−a, 0, b). In other words, when viewed from a camera positioned along the z-axis, the three points appear to form a straight line, with one point midway between the other two. Now suppose that the x-axis is rotated by an angle θx about the origin point (0, 0, 0). The other two points rotate to coordinates (a,−b sin θx,b cos θx) and (−a,−b sin θx,b cos θx). Compared to their original positions, these two points appear on the camera to have shifted in y by −b sin θx. As an example, let the photosensitive array in the camera have a linear dimension L=5 mm, NT=1000 pixels, and distance g=100 mm from the camera origin. Let the target be located at a distance h=1000 mm from the camera origin. Let the probe have a depth dimension b=25 mm. Assuming that the effective subpixel accuracy when usingtarget 1200 is dN= 1/141 as discussed above, the accuracy in determining the rotation of the target about the target's x-axis is approximately -
- Now consider the case in which the target is rotated about the y-axis by the angle θy. For the same conditions described above, if the rotation is about the origin point, the other two points both appear to shift in the x direction by approximately b sin θy. In other words, in the x-y plane of the camera, the origin point appears to move closer to one of the points than the other. For this case, the uncertainty in the measurement of the rotation angle θy is approximately the same as for rotation about θx, or approximately 14 microradians.
- For the case in which the target is rotated about the z-axis by the angle θz, consider a specific example. If the target image subtends all 1000 pixels in a 1000 pixel CCD array when R0=1 meter, then the uncertainty in the measurement of the angle θz when the target is 1 meter from the lens is
-
- which is the same uncertainty as for the orientation angles in the x and y directions.
- The uncertainty in the orientation (pitch, roll, and yaw) angles is multiplied by the distance from the origin of target to the point that is to be determined, which might be the tip of a probe or the tip of a tool such as a drill. For example, if a drill tip is located on an
end effector 400 at a distance 200 mm below the center oftarget 200B, the uncertainty in the position of the drill tip in relation to the target is approximately 14 ppm multiplied by 0.2 meter, which is 2.8 micrometers. - Because of the small uncertainties in the rotation angles, it is possible to attach the target a long distance from the tip of a machine tool or a long distance from the tip of a probe without significantly degrading accuracy. For the sake of clarity, the uncertainty in the position of such a tip with respect to the target will be called “relative tip position” uncertainty.
- A convenient method for determining the x-y-z coordinates of a machine tool, probe tip, or fiducial marker is to determine the coordinates of the target point relative to an arbitrary origin point. A best-fit calculation is then carried out to determine the distance to the origin point and the three rotation angles θx, θy, and θz. Finally, this information is used to calculate the position of the machine tool, probe tip, or fiducial marker.
- To determine the angle of the origin point on the target, an angular correction is added to the angles indicated by
angle meters target 1200 of 1/141, the uncertainty in the correction value is 0.35 microradian, which is a very small uncertainty. The uncertainty in the angular measurement of a gimbal system includes uncertainty components from the angular encoders, bearings, kinematic compensation, and angular correction as described above. If the angular bearings are of high quality and the kinematic compensation is suitable, then with high quality angular encoders the total angular error of 5 to 10 microradians is possible. This is equivalent to saying that the accuracy of the angular encoder is 5 to 10 μm/m or 5 to 10 ppm. Under these conditions, the angular correction component of the angular uncertainty is negligible. - The overall uncertainty in the coordinates of a point in a fixed position relative to the target is affected by (1) radial distance uncertainty, (2) angular distance uncertainty, (3) kinematic uncertainty, and (4) “relative tip position” uncertainty. Kinematic uncertainty refers to uncertainty associated with kinematic parameters such as R0 (distance from gimbal point to reference point on the instrument), Axis Offset (distance between mechanical axes at the point of closest approach), Axis Non-squareness (angle between the two mechanical axes with respect to 90 degrees), and so forth. With the properly designed target, good electrical, mechanical, and optical design, and good compensation, the uncertainty components are approximately (1) 7-14 ppm in radial distance, (2) 5-10 ppm in side-to-side (angular) distance, and (3) 1-2 ppm in kinematic effects. The uncertainty in the relative tip position is approximately 14 ppm, but this value is multiplied by the distance from the target to the probe tip rather than by the distance from the target to the tracker. For this reason, the uncertainty in the relative tip position is usually small and can be ignored. Radial and angular uncertainties are approximately equal, which will result in an uncertainty region in space that is approximately spherical and about 7-14 ppm in radius.
- As a specific example of how this relative uncertainty is converted into an absolute uncertainty, consider the case in which a target is measured at 3 meters with a relative uncertainty of 10 ppm. The uncertainty in the position of the target is then 3 m·10 μm/m=30 μm, which is a little more than 0.001 inch. For control of a robot drilling machine, an uncertainty of 150-200 micrometers is considered adequate in most cases. The device described here therefore has the accuracy required for this application. Furthermore, the simplicity of the design makes a low-cost, metrology-grade instrument available for the first time.
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Publication number | Priority date | Publication date | Assignee | Title |
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US9772394B2 (en) | 2010-04-21 | 2017-09-26 | Faro Technologies, Inc. | Method and apparatus for following an operator and locking onto a retroreflector with a laser tracker |
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US8619265B2 (en) | 2011-03-14 | 2013-12-31 | Faro Technologies, Inc. | Automatic measurement of dimensional data with a laser tracker |
US9377885B2 (en) | 2010-04-21 | 2016-06-28 | Faro Technologies, Inc. | Method and apparatus for locking onto a retroreflector with a laser tracker |
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CN102179726B (en) * | 2011-03-24 | 2016-06-29 | 哈尔滨理工大学 | Digital control processing secondary clamping deviation measuring apparatus and method based on image technique |
CN102155918B (en) * | 2011-03-28 | 2012-09-19 | 中国科学院长春光学精密机械与物理研究所 | Device and method for measuring five-DOF (degree of freedom) motion parameters of flexible jet pipes |
US9482529B2 (en) | 2011-04-15 | 2016-11-01 | Faro Technologies, Inc. | Three-dimensional coordinate scanner and method of operation |
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US9164173B2 (en) | 2011-04-15 | 2015-10-20 | Faro Technologies, Inc. | Laser tracker that uses a fiber-optic coupler and an achromatic launch to align and collimate two wavelengths of light |
US9686532B2 (en) | 2011-04-15 | 2017-06-20 | Faro Technologies, Inc. | System and method of acquiring three-dimensional coordinates using multiple coordinate measurement devices |
RU2472276C1 (en) * | 2011-07-22 | 2013-01-10 | Федеральное государственное бюджетное образовательное учреждение высшего профессионального образования "Уфимский государственный авиационный технический университет" | Linear step motor (versions) |
EP2557391A1 (en) | 2011-08-12 | 2013-02-13 | Leica Geosystems AG | Measuring device for determining the spatial location of a measuring aid |
US9222771B2 (en) | 2011-10-17 | 2015-12-29 | Kla-Tencor Corp. | Acquisition of information for a construction site |
EP2602641B1 (en) * | 2011-12-06 | 2014-02-26 | Leica Geosystems AG | Laser tracker with position-sensitive detectors for searching a target |
GB2498333A (en) * | 2011-12-21 | 2013-07-17 | Rolls Royce Plc | Measurement fixture for use in determining position and orientation of object and method of determining position, orientation of object relative to reference |
WO2013112455A1 (en) | 2012-01-27 | 2013-08-01 | Faro Technologies, Inc. | Inspection method with barcode identification |
KR20130102400A (en) * | 2012-03-07 | 2013-09-17 | 삼성전자주식회사 | Time of flight sensor and time of flight camera |
CN102607464B (en) * | 2012-03-30 | 2014-09-24 | 中国科学技术大学 | Auxiliary device for large surface shape measurement based on laser tracker and measurement method |
CN103376076A (en) * | 2012-04-23 | 2013-10-30 | 鸿富锦精密工业(深圳)有限公司 | Three-dimensional probe compensation and space error measuring system and method |
US20140000516A1 (en) * | 2012-06-29 | 2014-01-02 | Toyota Motor Engineering & Manufacturing North America, Inc. | Digital point marking transfer |
CN103009388B (en) * | 2012-11-05 | 2015-05-27 | 肖林 | Light wave transmitter as well as robot track locating system and robot track locating method |
KR101360028B1 (en) | 2012-12-17 | 2014-02-11 | 한국과학기술원 | Measuring device for 6 dof motion based on laser sensor through optimaization design |
US9046360B2 (en) | 2013-03-14 | 2015-06-02 | Faro Technologies, Inc. | System and method of acquiring three dimensional coordinates using multiple coordinate measurement devices |
US9188430B2 (en) | 2013-03-14 | 2015-11-17 | Faro Technologies, Inc. | Compensation of a structured light scanner that is tracked in six degrees-of-freedom |
US9041914B2 (en) | 2013-03-15 | 2015-05-26 | Faro Technologies, Inc. | Three-dimensional coordinate scanner and method of operation |
JP6097123B2 (en) * | 2013-04-02 | 2017-03-15 | 株式会社ミツトヨ | 3D measurement system |
JP6097624B2 (en) * | 2013-04-02 | 2017-03-15 | 株式会社ミツトヨ | 3D measurement system |
EP2801841B1 (en) * | 2013-05-10 | 2018-07-04 | Leica Geosystems AG | Laser tracker with a target detecting unit for a target tracking system and orientation detection |
US9857160B1 (en) | 2013-09-24 | 2018-01-02 | TVS Holdings, LLC | Multi-mode frequency sweeping interferometer and method of using same |
US9395174B2 (en) | 2014-06-27 | 2016-07-19 | Faro Technologies, Inc. | Determining retroreflector orientation by optimizing spatial fit |
US9976947B1 (en) | 2014-11-24 | 2018-05-22 | TVS Holdings, LLC | Position measurement device |
US20170094251A1 (en) * | 2015-09-30 | 2017-03-30 | Faro Technologies, Inc. | Three-dimensional imager that includes a dichroic camera |
CN105249613B (en) * | 2015-11-11 | 2018-05-25 | 吴志龙 | The method and device of shoes inner space acquisition |
AU2017294796B2 (en) | 2016-07-15 | 2019-05-30 | Fastbrick Ip Pty Ltd | Brick/block laying machine incorporated in a vehicle |
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DE102016118616B4 (en) * | 2016-09-30 | 2018-11-22 | Carl Zeiss Industrielle Messtechnik Gmbh | Measuring device for an optical measuring system |
RU2672807C2 (en) * | 2017-02-17 | 2018-11-19 | Общество С Ограниченной Ответственностью "Фиттин" | Method for measuring shape, dimensions and elastic properties of inner surface hollow objects, method for constructing three-dimensional model of internal surfaces hollow objects, device for measuring shape, dimensions and elastic properties of inner surface hollow objects and constructing three-dimensional model of internal surfaces hollow objects |
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AU2018295572B2 (en) | 2017-07-05 | 2022-09-29 | Fastbrick Ip Pty Ltd | Real time position and orientation tracker |
US10247542B2 (en) | 2017-08-09 | 2019-04-02 | Leica Geosystems Ag | Handheld measuring aid with a 3-axis joint connection and a spherical encoder |
CN111226090B (en) | 2017-08-17 | 2023-05-23 | 快砖知识产权私人有限公司 | Laser tracker with improved roll angle measurement |
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ES2971624T3 (en) | 2017-10-11 | 2024-06-06 | Fastbrick Ip Pty Ltd | Machine for transporting objects |
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US11619481B2 (en) | 2018-08-13 | 2023-04-04 | Faro Technologies, Inc. | Coordinate measuring device |
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CN110440692B (en) * | 2019-08-27 | 2020-10-20 | 大连理工大学 | Combined measurement and calibration method of laser tracker and structured light 3D scanner |
TWI726536B (en) | 2019-12-16 | 2021-05-01 | 財團法人工業技術研究院 | Image capturing method and image capturing apparatus |
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EP4332495A1 (en) | 2022-09-01 | 2024-03-06 | Leica Geosystems AG | Measuring instrument with a scanning absolute distance meter |
CN116379925A (en) * | 2022-12-12 | 2023-07-04 | 深圳市中图仪器股份有限公司 | Six-dimensional laser tracking measurement system with active back tracking function |
CN118209087B (en) * | 2024-05-16 | 2024-07-23 | 晓智未来(成都)科技有限公司 | Space point and plane positioning calibration method based on photogrammetry |
Citations (9)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4396945A (en) * | 1981-08-19 | 1983-08-02 | Solid Photography Inc. | Method of sensing the position and orientation of elements in space |
US4714339A (en) * | 1986-02-28 | 1987-12-22 | The United States Of America As Represented By The Secretary Of Commerce | Three and five axis laser tracking systems |
US4790651A (en) * | 1987-09-30 | 1988-12-13 | Chesapeake Laser Systems, Inc. | Tracking laser interferometer |
US5196900A (en) * | 1988-04-12 | 1993-03-23 | Metronor A.S. | Method and sensor for opto-electronic angle measurements |
US5440392A (en) * | 1991-10-11 | 1995-08-08 | Metronor As | Method and system for point by point measurement of spatial coordinates |
US5973788A (en) * | 1995-10-12 | 1999-10-26 | Metronor Asa | System for point-by-point measuring of spatial coordinates |
US6279246B1 (en) * | 1997-04-21 | 2001-08-28 | N.V. Krypton Electronic Engineering | Device and method for determining the position of a point |
US20020048027A1 (en) * | 1993-05-24 | 2002-04-25 | Alf Pettersen | Method and system for geometry measurements |
US20040136012A1 (en) * | 2002-11-15 | 2004-07-15 | Leica Geosystems Ag | Method and device for calibrating a measuring system |
Family Cites Families (6)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPH05306907A (en) * | 1992-04-30 | 1993-11-19 | Suzuki Motor Corp | Lens measurement control system |
JPH0795598A (en) * | 1993-09-25 | 1995-04-07 | Sony Corp | Object tracking device |
JPH10294890A (en) * | 1997-04-21 | 1998-11-04 | Nippon Hoso Kyokai <Nhk> | Automatic/manual photographic camera system |
US6973202B2 (en) * | 1998-10-23 | 2005-12-06 | Varian Medical Systems Technologies, Inc. | Single-camera tracking of an object |
JP4444746B2 (en) * | 2003-07-22 | 2010-03-31 | 株式会社日立国際電気 | Object tracking method and object tracking device |
JP5123932B2 (en) * | 2006-04-21 | 2013-01-23 | ファロ テクノロジーズ インコーポレーテッド | Camera-equipped 6-degree-of-freedom target measurement device and target tracking device with a rotating mirror |
-
2007
- 2007-04-20 JP JP2009506588A patent/JP5127820B2/en not_active Expired - Fee Related
- 2007-04-20 DE DE602007011045T patent/DE602007011045D1/en active Active
- 2007-04-20 US US11/738,005 patent/US7576836B2/en active Active
- 2007-04-20 WO PCT/US2007/009593 patent/WO2007124010A2/en active Application Filing
- 2007-04-20 CN CN200780014088.0A patent/CN101427153B/en not_active Expired - Fee Related
- 2007-04-20 EP EP07755744A patent/EP2008120B1/en not_active Revoked
Patent Citations (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US4396945A (en) * | 1981-08-19 | 1983-08-02 | Solid Photography Inc. | Method of sensing the position and orientation of elements in space |
US4714339A (en) * | 1986-02-28 | 1987-12-22 | The United States Of America As Represented By The Secretary Of Commerce | Three and five axis laser tracking systems |
US4714339B1 (en) * | 1986-02-28 | 1997-03-18 | Us Army | Three and five axis laser tracking systems |
US4714339B2 (en) * | 1986-02-28 | 2000-05-23 | Us Commerce | Three and five axis laser tracking systems |
US4790651A (en) * | 1987-09-30 | 1988-12-13 | Chesapeake Laser Systems, Inc. | Tracking laser interferometer |
US5196900A (en) * | 1988-04-12 | 1993-03-23 | Metronor A.S. | Method and sensor for opto-electronic angle measurements |
US5440392A (en) * | 1991-10-11 | 1995-08-08 | Metronor As | Method and system for point by point measurement of spatial coordinates |
US20020048027A1 (en) * | 1993-05-24 | 2002-04-25 | Alf Pettersen | Method and system for geometry measurements |
US5973788A (en) * | 1995-10-12 | 1999-10-26 | Metronor Asa | System for point-by-point measuring of spatial coordinates |
US6279246B1 (en) * | 1997-04-21 | 2001-08-28 | N.V. Krypton Electronic Engineering | Device and method for determining the position of a point |
US20040136012A1 (en) * | 2002-11-15 | 2004-07-15 | Leica Geosystems Ag | Method and device for calibrating a measuring system |
Cited By (40)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
US20100049354A1 (en) * | 2006-04-28 | 2010-02-25 | Ulrich Stark | Method and Apparatus for Ensuring the Dimensional Constancy of Multisegment Physical Structures During Assembly |
US8082052B2 (en) * | 2006-04-28 | 2011-12-20 | Airbus Deutschland Gmbh | Method and apparatus for ensuring the dimensional constancy of multisegment physical structures during assembly |
US20090268214A1 (en) * | 2006-05-26 | 2009-10-29 | Miljenko Lucic | Photogrammetric system and techniques for 3d acquisition |
US20090214106A1 (en) * | 2008-02-26 | 2009-08-27 | Caterpillar Inc. | Photogrammetric target and related method |
US8094321B2 (en) * | 2008-02-26 | 2012-01-10 | Caterpillar Inc. | Photogrammetric target and related method |
US20100283854A1 (en) * | 2008-05-12 | 2010-11-11 | Flir Systems, Inc. | Optical Payload Electrical System |
US8269893B2 (en) * | 2008-05-12 | 2012-09-18 | Flir Systems, Inc. | Optical payload electrical system |
WO2012076400A1 (en) * | 2010-12-08 | 2012-06-14 | Robert Bosch Gmbh | Camera-based method for distance determination in a stationary vehicle |
EP2508428A1 (en) | 2011-04-08 | 2012-10-10 | Thales Alenia Space Italia S.p.A. | Coarse and fine projective optical metrology system |
US8625108B2 (en) | 2011-04-08 | 2014-01-07 | Thales Alenia Space Italia S.P.A. Con Unico Socio | Protective optical metrology system for determining attitude and position |
ITTO20110325A1 (en) * | 2011-04-08 | 2012-10-09 | Thales Alenia Space Italia S P A C On Unico Socio | METROLOGICAL OPTICAL PROJECTIVE SYSTEM FOR THE DETERMINATION OF TRIM AND POSITION |
EP2508427A1 (en) | 2011-04-08 | 2012-10-10 | Thales Alenia Space Italia S.p.A. | Projective optical metrology system for determining attitude and position |
US20120261513A1 (en) * | 2011-04-08 | 2012-10-18 | Thales Alenia Space Italia S.P.A. Con Unico Socio | Coarse and fine projective optical metrology system |
US8724104B2 (en) * | 2011-04-08 | 2014-05-13 | Thales Alenia Space Italia S.P.A. Con Unico Socio | Coarse and fine projective optical metrology system |
ITTO20110323A1 (en) * | 2011-04-08 | 2012-10-09 | Thales Alenia Space Italia S P A C On Unico Socio | OPTICAL METROLOGICAL SYSTEM, LARGE AND PRECISION PROJECTIVE |
US20130113897A1 (en) * | 2011-09-25 | 2013-05-09 | Zdenko Kurtovic | Process and arrangement for determining the position of a measuring point in geometrical space |
US20130253871A1 (en) * | 2012-03-20 | 2013-09-26 | Hurco Companies, Inc. | Method for measuring a rotary axis of a machine tool system |
US9784554B2 (en) * | 2012-03-20 | 2017-10-10 | Hurco Companies, Inc. | Method for measuring a rotary axis of a machine tool system |
US20140132729A1 (en) * | 2012-11-15 | 2014-05-15 | Cybernet Systems Corporation | Method and apparatus for camera-based 3d flaw tracking system |
EP2801839A1 (en) * | 2013-05-10 | 2014-11-12 | Leica Geosystems AG | Handheld measuring aid for use with a 6-DoF laser tracker |
US9816813B2 (en) | 2013-05-10 | 2017-11-14 | Leica Geosystems Ag | Handheld measuring aid for use with a six-degrees-of-freedom laser tracker |
US20150015700A1 (en) * | 2013-07-03 | 2015-01-15 | Faro Technologies, Inc. | Laser tracker that cooperates with a remote camera bar and coordinate measurement device |
US9476695B2 (en) * | 2013-07-03 | 2016-10-25 | Faro Technologies, Inc. | Laser tracker that cooperates with a remote camera bar and coordinate measurement device |
DE102014012693A1 (en) * | 2014-09-01 | 2016-03-03 | Hochschule RheinMain University of Applied Sciences Wiesbaden Rüsselsheim Geisenheim | System for position and orientation of objects |
DE102014012693B4 (en) * | 2014-09-01 | 2019-11-14 | Hochschule RheinMain University of Applied Sciences Wiesbaden Rüsselsheim Geisenheim | System and method and computer program for position and position determination of objects |
CN105425827A (en) * | 2015-11-05 | 2016-03-23 | 中国船舶重工集团公司第七二四研究所 | Auxiliary positioning device and method for adjustable radar feed source |
US10753723B2 (en) | 2015-11-09 | 2020-08-25 | Björn Habrich | Method and device for determining the spatial position of an object by means of interferometric length measurement |
WO2017081017A1 (en) * | 2015-11-09 | 2017-05-18 | Björn Habrich | Method and device for determining the spatial position of an object by means of interferometric length measurement |
CN105547172A (en) * | 2016-01-06 | 2016-05-04 | 上海大学 | System and method for measuring repeatability precision of industrial robot on the basis of acupuncture luminescence method |
US20170210011A1 (en) * | 2016-01-22 | 2017-07-27 | The Boeing Company | Apparatus and Method to Optically Locate Workpiece for Robotic Operations |
US9815204B2 (en) * | 2016-01-22 | 2017-11-14 | The Boeing Company | Apparatus and method to optically locate workpiece for robotic operations |
IT201600107650A1 (en) * | 2016-10-25 | 2018-04-25 | Torino Politecnico | Feeler device and localization procedure of a feeler device for the measurement of large objects |
EP3557182A1 (en) * | 2018-04-20 | 2019-10-23 | CSEM Centre Suisse d'Electronique et de Microtechnique SA - Recherche et Développement | Positioning system and method |
DE102019114531B4 (en) * | 2019-05-29 | 2021-06-17 | Soft2Tec Gmbh | Device for position and position detection of markings in three-dimensional space |
US10989671B2 (en) * | 2019-09-16 | 2021-04-27 | The Boeing Company | Method and system for determining alignment and orientation of a target |
WO2021259523A1 (en) | 2020-06-25 | 2021-12-30 | Soft2Tec Gmbh | Apparatus for detecting the location and position of markings, and computer program product |
US11815345B2 (en) | 2020-06-25 | 2023-11-14 | Soft2Tec Gmbh | Device for orientation and position detection of markings in three-dimensional space |
DE102020118407A1 (en) | 2020-07-13 | 2022-01-13 | Soft2Tec Gmbh | Device and method for detecting the orientation and position of markings in three-dimensional space |
WO2022012899A2 (en) | 2020-07-13 | 2022-01-20 | Soft2Tec Gmbh | Device and method for detecting the location and position of markings in three-dimensional space |
CN116124010A (en) * | 2022-11-21 | 2023-05-16 | 富视达技术(武汉)有限公司 | Visual displacement measurement system and method |
Also Published As
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WO2007124010A2 (en) | 2007-11-01 |
JP2009534658A (en) | 2009-09-24 |
CN101427153A (en) | 2009-05-06 |
CN101427153B (en) | 2013-02-27 |
WO2007124010A3 (en) | 2008-01-17 |
EP2008120B1 (en) | 2010-12-08 |
EP2008120A2 (en) | 2008-12-31 |
JP5127820B2 (en) | 2013-01-23 |
US7576836B2 (en) | 2009-08-18 |
DE602007011045D1 (en) | 2011-01-20 |
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